Patent Publication Number: US-8967426-B2

Title: Medicine feeder and medicine dispenser

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a medicine feeder for storing tablets, capsules or other solid-type medicines by the kind and dispensing these medicines one by one in predetermined numbers based on prescription information. The invention also relates to a medicine dispenser including a plurality of the medicine feeders. 
     2. Description of the Related Art 
     A dispenser of solid medicines (hereinafter simply called “tablet(s)”), includes a predetermined number of cassette-type medicine feeders for dispensing tablets one by one. In the medicine feeder, a medicine storage has a bottom provided with a rotor. The rotor has an outer circumferential surface formed with a large number of pockets, and as the rotor rotates, tablets in the medicine storage are dispensed one by one from a dispensing spout (Japanese Patent Laid-Open No. 2005-289506). 
     In this dispensing process in the medicine dispenser, there are cases where a tablet becomes jammed resulting in seizing and disabling of the rotor due to a trouble caused by, for example, the shape of the tablet or the tablet&#39;s attitude at the time of entering the pocket in the outer circumference of the rotor. 
     When jamming of a tablet is detected, the state of clogging can be cleared by a known method: Upon detection of an overcurrent to a DC motor which drives the rotor, a determination is made that the motor has been locked by a jammed tablet and the motor is driven in a reverse direction momentarily (Japanese Patent Laid-Open No. 2000-103404). 
     Another known method is counting the quantity of tablets being dispensed and reversing the rotor momentarily upon a determination that the counting within a predetermined period of time gives a smaller number than predetermined due to a jammed tablet (Japanese Patent No. 3895989). 
     In whichever of the cases, reverse rotation of the rotor is achieved by inverting the polarity of electric current supplied to the motor. 
     SUMMARY OF THE INVENTION 
     1. Problems to be Solved by the Invention 
     However, reversing the motor rotation by inverting the polarity of the motor current as used in the conventional methods in order to reverse the rotation of the rotor has a problem since the motor is subjected to a strong torque at the time of reversing the rotation, and repeating such a cycle of normal-and-reverse rotations will lead to a problem of reduced life of the motor. 
     It is therefore an object of the present invention to solve the problem of jammed tablets in medicine feeders and in a medicine dispenser including the medicine feeders, through improvements on a motor drive unit which drives the rotor of the dispensing cassettes so that reverse rotation of the rotor can be achieved without rotating the motor in reverse, i.e. by reversing only the rotor while the motor remains in a normal rotation setting, in cases where a jammed tablet is detected. 
     2. Means for Solving the Problems 
     In order to solve the above-described problem, the present invention includes an aspect relating to a medicine feeder, and offers a medicine feeder which is provided by a combination of a dispensing cassette and a drive unit. The dispensing cassette includes a medicine storage for storing medicine, and a rotor at a bottom portion of the medicine storage. The drive unit includes a drive motor, a gear transmission device, an output shaft and a switcher. The gear transmission device has a normal-rotation transmission path and a reverse-rotation transmission path constituted by gear trains between a motor shaft of the drive motor and the output shaft. The switcher selects one of the transmission paths for an output of driving power from the drive motor to the dispensing cassette. 
     In the medicine feeder described above, when the drive unit drives the dispensing cassette, the drive power is transmitted via the normal-rotation transmission path, thereby driving the rotor in a normal rotation direction, to dispense a tablet. Upon detection of trouble such as a jammed tablet, the switcher switches the drive power transmission path to the reverse-rotation transmission path, and thereby the motor remains in the normal rotation setting but the rotor is driven in a reverse rotation direction in an attempt to clear the jammed tablet. 
     Also, in order to solve the above-described problem, the present invention includes an aspect relating to a medicine dispenser, and offers a medicine dispenser which includes a predetermined number of medicine feeders, a control circuit and a display device. The medicine feeder is provided by a combination of a medicine dispensing cassette and a drive unit. The dispensing cassette includes a medicine storage for storing medicine, and a rotor at a bottom portion of the medicine storage. The drive unit includes a drive motor, a gear transmission device, an output shaft, a switcher, a tablet counting sensor and a rotor-rotation detection sensor. The gear transmission device has a normal-rotation transmission path and a reverse-rotation transmission path between a motor shaft of the drive motor and the output shaft. The switcher selects one of the transmission paths for an output of driving power from the drive motor to the dispensing cassette. Upon detection of a stoppage of the rotor based on a signal from the rotor-rotation detection sensor, the control circuit controls the drive unit for reverse rotation of the rotor for a predetermined period of time followed by resumption to normal rotation. 
     3. Advantages of the Invention 
     As described, in cases where a tablet is jammed, the medicine feeder and the medicine dispenser according to the present invention are capable of attempting to clear the jammed tablet by driving the rotor in a reverse rotation direction without making the drive motor rotate in a reverse rotation direction. Since the motor is not driven in a reverse rotation direction, the motor can work under a reduced burden, and can have an extended life according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a medicine dispenser according to a first embodiment. 
         FIG. 2  is a sectional view of the medicine feeder. 
         FIG. 3  is a perspective view of a vertical section of a rotor region in the medicine feeder. 
         FIG. 4  is a simplified plan view of a horizontal section taken along lines X 1 -X 1  in  FIG. 2 . 
         FIG. 5  is a perspective view of a drive unit. 
         FIG. 6  is a sectional view taken along lines X 2 -X 2  in  FIG. 5 . 
         FIG. 7  is a sectional view taken along lines X 3 -X 3  in  FIG. 6 . 
         FIG. 8  is a schematic illustration of a gear train in normal rotation transmission. 
         FIG. 9  is a side view of a vertical section taken in  FIG. 8 . 
         FIG. 10  is an explanatory drawing of a gear train in reverse rotation transmission. 
         FIG. 11  is a side view of a vertical section taken along  FIG. 10 . 
         FIG. 12  is a front view of a rotor-rotation detection sensor. 
         FIG. 13  is a control block diagram of the medicine dispenser according to the first embodiment. 
         FIG. 14  is a flowchart for the first embodiment. 
         FIG. 15  is a flowchart for the first embodiment, for normal rotation of the rotor. 
         FIG. 16  is a flowchart for the first embodiment, for reverse rotation of the rotor. 
         FIG. 17  is a sectional view of a drive unit according to a second embodiment. 
         FIG. 18  is a sectional view taken along lines X 4 -X 4  in  FIG. 17 . 
         FIG. 19  is an explanatory drawing of a gear train in normal rotation transmission. 
         FIG. 20  is a side view of a vertical section taken in  FIG. 19 . 
         FIG. 21  is an explanatory drawing of a gear train in reverse rotation transmission. 
         FIG. 22  is a side view of a vertical section taken in  FIG. 20 . 
         FIG. 23  is a simplified sectional view of a third embodiment. 
         FIG. 24A  is an enlarged sectional view of a clutch region in  FIG. 23 . 
         FIG. 24B  is an enlarged partial plan view of a male spline in  FIG. 23 . 
         FIG. 25  is a simplified sectional view of a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described based on the attached drawings. 
     First Embodiment 
     As shown in  FIG. 1 , a medicine dispenser  11  according to a first embodiment incorporates a large number of medicine feeders  13  (see  FIG. 2 ) behind a front door  12 . Also, an operation display panel  14  is provided on the right of the door  12 . 
     As shown in  FIG. 2 , the medicine feeder  13  is composed of a dispensing cassette  16  and a drive unit  17 . The dispensing cassette  16  is conventional (see Japanese Patent Laid-Open No. 2005-289506), and includes a medicine storage  18  which stores tablets, a rotor  19  provided at a bottom of the medicine storage  18 , a gear transmission section  21  provided at a bottom surface of the medicine storage  18 , and other components. 
     Drive power from the drive unit  17  is transmitted via the gear transmission section  21  to rotate the rotor  19 , and in this rotation, tablets T (see  FIG. 3 ) in the medicine storage  18  are distributed into pockets  22  between a large number of vertical ribs  20  provided in an outer circumferential surface of the rotor  19 . Near a dispensing spout  23 , a partitioning member  24 , which is like a comb having elastic bristle teeth, is inserted from a slit  24   a  across the pocket  22  as indicated by Arrow “a”, so that there is only one tablet T below the partitioning member  24 . This singularly isolated tablet T is dispensed into a container or the like upon coming to the dispensing spout  23 . The dispensing spout  23  is provided with an optical, tablet counting sensor  25  which includes a light emitter and a light receiver. 
     The gear transmission section  21  is composed of a worm gear  27  attached to an input shaft  26 ; a worm ring  28  engaged therewith; and a rotor gear  29  engaged with the worm ring  28 . In the case shown in the Figure, the worm gear  27  has a right-hand helix (see  FIG. 4 ). The input shaft  26  is connectable with and disconnectable from an output shaft  31  (see  FIG. 4 ) of the drive unit  17  via couplings  32 ,  33 . 
       FIG. 4  shows rotation directions of the gears  27 ,  28  and  29  as viewed from a line X 1 -X 1  in  FIG. 2 . In the Figure, Arrow A indicates clockwise rotation, i.e., normal rotation, whereas Arrow B indicates counterclockwise rotation, i.e., reverse rotation.  FIG. 4  shows a dispensing state in which the rotor gear  29  is rotating normally, causing normal rotation of a rotor shaft  30  and the rotor  19  which is integral therewith. 
     In this case, when the input shaft  26  rotates in a reverse direction, the worm gear  27 , which has a right-hand helix as described above, causes the worm ring  28  to rotate in a reverse direction, so the rotor gear  29  and the rotor shaft  30  make normal rotation. The statement that the input shaft  26  makes reverse rotation means that the input shaft  26  makes counterclockwise rotation as indicated by Arrow B when the drive-source side is viewed from the load side as shown by white Arrow E. 
     As defined above, in the present specification, the direction of rotation of any rotating member will be based on a view obtained when the drive-source side is viewed from the load side: Clockwise rotation will be called normal rotation and indicated by a letter A whereas counterclockwise rotation will be called reverse rotation and indicated by a letter B. 
     The dispensing cassette  16  has the gear transmission section  21  as described so far. Thus, in order to cause normal rotation of the rotor  19  for dispensing a tablet, it is necessary to provide a reverse-rotation input to the input shaft  26 , and on the contrary, in order to make reverse rotation of the rotor  19 , it is necessary to make a normal-rotation input to the input shaft  26 . 
     As shown in  FIG. 5 , the drive unit  17  has a bearing sleeve  37 , which protrudes from a lid case  35 . The output shaft  31  has its tip portion inserted into the bearing sleeve  37 . The coupling  32  is attached to the tip portion of the output shaft  31 . The drive unit  17  has four mounting tabs  35   a  along a side edge of the lid case  35 , and is fixed to the dispenser  11  by screwing to an appropriate position in the dispenser  11  so that the output shaft  31  is oriented in the forward direction. 
     When a dispensing cassette  16 , which is to be combined with the drive unit  17 , is inserted horizontally from the front of the dispenser  11  (see Arrow “a” in  FIG. 4 ), the output shaft  31  of the drive unit  17  and the input shaft  26  of the dispensing cassette  16  are connected with each other via the coupling  32 ,  33 . 
     As shown in  FIG. 5 , the drive unit  17  includes a main body case  34  which has an open end; a lid case  35  which closes the open end; and a cover case  36  which covers a closed end of the main body case  34 . The bearing sleeve  37  is provided in the lid case  35  so as to protrude therefrom, and as described earlier, the output shaft  31  has its tip portion inserted into the bearing sleeve  37 . The lid case  35  has a lead wire insertion hole  40  for electric components disposed therein. 
     As shown in  FIG. 6 , the drive unit  17  has two kinds of DC motors, i.e., a drive motor  38  and a switching motor  39 . These motors  38 ,  39  are disposed so that their motor shafts  41 ,  42  (see  FIG. 7 ) are perpendicular to each other. The drive motor  38  takes one of two states; normal rotation and stop. This motor is not controlled to rotate in a reverse direction. The switching motor  39  is controlled to make whichever of normal and reverse rotations. 
     The drive motor  38  is mounted to a back surface of the main body case  34  and is covered by the cover case  36 . The motor shaft  41  of the drive motor  38  protrudes into the main body case  34 , and a drive gear  43  is mounted to the protruding portion. Also, the output shaft  31  is mounted with an output gear  44 . The output shaft  31  penetrates the closed end surface of the main body case  34 , with a rear end reaching inside the cover case  36 . 
     As shown in  FIG. 6 , a gear transmission device  60  which includes the above-described drive gear  43  and output gear  44  is provided between the motor shaft  41  and the output shaft  31 . The gear transmission device  60  includes a plurality of gears and provides thereby, two transmission paths, i.e., a normal-rotation transmission path  45  (see  FIG. 7  and  FIG. 8 ) and a reverse-rotation transmission path  46  (see  FIG. 7  and  FIG. 10 ). 
     The drive gear  43 , the output gear  44  and a switching gear  47  work in both of the transmission paths  45 ,  46  as common members. This simplifies the transmission paths. The switching gear  47  is always in engagement with the drive gear  43 , and as will be described later, can be switched to belong to the normal-rotation transmission path  45  or to belong to the reverse-rotation transmission path  46  by a switcher which includes the switching motor  39 . 
       FIG. 6  and  FIG. 7  show a case where the switching gear  47  belongs to the normal-rotation transmission path  45 . In  FIG. 8  and  FIG. 9 , the normal-rotation transmission path  45  is highlighted by not illustrating the reverse-rotation transmission path  46 . 
     The normal-rotation transmission path  45  is provided by the drive gear  43 , the switching gear  47 , a middle gear  48  and the output gear  44  engaged mutually one after another. As shown in  FIG. 8 , the middle gear  48  is a two-stage gear, having a large-diameter wheel  48   a  engaged with the switching gear  47 , and a small-diameter wheel  48   b  engaged with the output gear  44 . With an even number (four) of gears, normal rotation of the drive motor  38  causes reverse rotation of the output gear  44 , and reverse rotation of the output shaft  31 . 
     As described, in the dispensing cassette  16 , which is connected with the output shaft  31 , reverse rotation of the input shaft  26  causes the rotor  19  to make normal rotation (see  FIG. 4 ). Thus, as the drive motor  38  makes normal rotation in the drive unit  17 , normal rotation drive power is transmitted via the normal-rotation transmission path  45  to the rotor  19 , and a tablet is dispensed. 
     On the other hand, if the switching motor  39  shifts the switching gear  47  to belong to the reverse-rotation transmission path  46  as will be described later, the reverse-rotation transmission path  46  is established by a gear train as shown in  FIG. 10 , including the drive gear  34 , the switching gear  47 , a first middle gear  49 , a second middle gear  50  and the output gear  44  which are engaged mutually one after another. Each of the first middle gear  49  and the second middle gear  50  is provided by a two-stage gear. The former has a large-diameter wheel  49   a  engaged with the switching gear  47 , and a small-diameter wheel  49   b  engaged with a large-diameter wheel  50   a  of the second middle gear  50 . The second middle gear  50  has a small-diameter wheel  50   b  engaged with the output gear  44 . 
     In this case, with an odd number (five) of the gears, normal rotation of the drive motor  38  makes normal rotation of the output gear  44 . As a result, in the dispensing cassette  16  which is connected with the output shaft  31 , the input shaft  26  makes normal rotation, and thereby the rotor  19  makes reverse rotation. In other words, normal-rotation drive power of the drive motor  38  is transmitted via the reverse-rotation transmission path  46  for reverse rotation of the rotor  19  to clear clogging of a tablet, for example. 
     Next, the normal-rotation transmission path  45  and the reverse-rotation transmission path  46  will be described in terms of their gear arrangement in gear axial direction. For the sake of description, gear axial positions will be divided into three layers as shown in  FIG. 6 , which will be called Layer “a”, Layer “b”, and Layer “c” starting from the side closest to the drive motor  38 . 
     First, the normal-rotation transmission path  45  will be described based on  FIG. 8  and  FIG. 9 . The drive gear  43  is in Layer “b” (see  FIG. 9 ). The drive gear  43  is always in engagement with the switching gear  47 , which is also in Layer “b”. The switching gear  47  engages with the middle gear  48 , which is a two-stage gear as described earlier, and its large-diameter wheel  48   a  is in Layer “b”, being in engagement with the switching gear  47 . The small-diameter wheel  48   b  is in Layer “c”. The small-diameter wheel  48   b  is in engagement with the output gear  44  which is also in Layer “c”. 
     Now, turning to the reverse-rotation transmission path  46 , as will be understood from  FIG. 6  and  FIG. 11 , the drive gear  43  and the switching gear  47  are in Layer “b” like in the previous case. The first middle gear  49  has its large-diameter wheel  49   a  in Layer “b” and in engagement with the switching gear  47  whereas the small-diameter wheel  49   b  is in Layer “a”. The second middle gear  50  has its large-diameter wheel  50   a  in Layer “a” and in engagement with the small-diameter wheel  49   b  of the first middle gear  49 . The small-diameter wheel  50   b  extends to Layer “c” for engagement with the output gear  44  in Layer “c”. The small-diameter wheel  50   b  of the second middle gear  50  has a smaller diameter than the output gear  44  for rotation at a predetermined speed reduction ratio. 
     A comparison between the normal-rotation transmission path  45  and the reverse-rotation transmission path  46  will reveal that the middle gear  48  in the former is essentially of the same size as the first middle gear  49  in the latter, and so the difference in the quantity of gears between the two gear trains  48 ,  49  is only one, i.e., whether or not the gear train has the second middle gear  50 . 
     In reverse rotation transmission, as shown in  FIG. 10 , the second middle gear  50  has its large-diameter wheel  50   a  in engagement with the first middle gear  49  in the previous stage while its small-diameter wheel  50   b  is in engagement with the output gear  44  in the next stage. Compared to the normal rotation transmission illustrated in  FIG. 8 , this gear arrangement has an additional speed reduction stage provided by the smaller-diameter wheel  50   b  and the larger-diameter output gear  44 . The arrangement provides a greater speed reduction ratio in the reverse rotation transmission than in the normal rotation transmission, providing a relatively greater reverse rotation torque concomitantly. 
     It should be noted here that in cases where the quantity of gears in the gear transmission section  21  (see  FIG. 4 ) of the dispensing cassette  16  is greater by one, or smaller by one, than the above-described case, direction of rotation will be opposite from the above-described case; i.e., inputting normal rotation to the input shaft  26  will cause the rotor  19  to make normal rotation. In this case, therefore, the above-described normal-rotation transmission path  45  in the drive unit  17  will function as a reverse-rotation transmission gear train, i.e. a reverse-rotation transmission path. Likewise, the reverse-rotation transmission path  46  will work as a normal-rotation transmission gear train, i.e., a normal-rotation transmission path. 
     In whichever of the cases, independent from the gear configuration of the gear transmission section  21  in the dispensing cassette  16 , the drive unit  17  has a normal-rotation transmission path for transmission of normal rotation to the rotor  19 , and a reverse-rotation transmission path for transmission of reverse rotation thereto; and switching is performed to select one of the gear trains so that the output shaft  31  makes normal rotation or reverse rotation. The gear train to be switched to will be determined by the gear configuration of the gear transmission section  21  in the dispensing cassette  16 . 
     Next, the switcher will be described. As shown in  FIG. 6  and  FIG. 7 , the switcher is composed of the switching motor  39  which is controlled to rotate in whichever of the normal and reverse directions; a worm gear  51  which is attached to a motor shaft  42  of the motor; and a worm ring  52 . The worm ring  52  has a rotation shaft  53 , which is separate from but coaxial with a drive shaft  41  of the drive motor  38 . As shown in  FIG. 6 , the worm ring  52  is in Layer “c” in terms of the axial position. 
     The worm ring  52  is formed with a cutout portion  54  (see  FIG. 7 ), which has a 90 degree center angle. A sector-shaped stopper  55  having a smaller center angle than the cutout portion  54  is formed in an inner surface of the lid case  35 . The stopper  55  protrudes into the cutout portion  54 . A rotation angle of the worm ring  52  is limited within a range of angle difference θ (see  FIG. 6 ) between the cutout portion  54  and the stopper  55 . The worm ring  52  functions as a rotation member whose rotation range is limited within the range of the angle difference θ. 
     The switching motor  39  is controlled so as to rotate the worm ring  52  in an angle range which is defined as a sum of the angle difference θ and a predetermined margin-angle. Thus, the worm ring  52  reliably makes contact with the stopper  55 , and stops. The arrangement ensures accurate setting of two, right and left stop positions of the switching gear  47 . 
     The switching motor  39  may be provided by a stepping motor. In such a case, the stopper  55  may be eliminated since stepping motors can provide highly accurate control on the rotation angle. 
     The switching gear  47  is rotatably supported by a shaft  56  in an end surface of the worm ring  52  which is the end surface closer to the drive motor  38 . As shown in  FIG. 8  and  FIG. 9 , at this position, the switching gear  47  has a rotation radius for engagement with the drive gear  43  in its circumferential direction. Also in the circumferential direction, this is a position for engagement with the middle gear  48 , under the state where the worm ring  52  is in stoppage after it has made right-hand rotation (see Arrow C in  FIG. 8 ) and has made contact with the stopper  55 . 
     The angle difference θ is set to a value, with which the switching motor  39  makes reverse rotation, causing the worm gear  51  and the worm ring  52  to make reverse rotation (see Arrow D in  FIG. 10 ) and subsequently causing the worm ring  52  to make contact with and to stop on the opposite surface of the stopper  55 , so that the switching gear  47  disengages from the middle gear  48  in the normal-rotation transmission path  45  and engages with the first middle gear  49  in the reverse-rotation transmission path  46 . 
     It should be noted here that the sector-shaped stopper  55  may be replaced by limit pins erected at two positions representing the two side surfaces of the stopper. 
     As shown in  FIG. 6 , the output shaft  31  penetrates into the cover case  36 , and the penetrating end of the shaft is provided with a rotor-rotation detection sensor  58 . As shown in  FIG. 12 , the rotor-rotation detection sensor  58  is provided by a two-phase pulse-output rotary encoder which is composed of a rotating plate  57  having a large number of slits  69 , and two optical sensors  59   a ,  59   b  for detecting light which passes through these slits  69 . Although the Figure shows that the sensors  59   a ,  59   b  are opposed to each other in a diametrical direction of the rotating plate  57 , sensor positions are not limited to this layout, and may be selected arbitrarily as long as a predetermined phase difference is obtained. 
     The sensors  59   a ,  59   b  output two, phase-different pulse signals to a control circuit  61  (see  FIG. 13 ) which is to be described later, and the control circuit  61  determines whether the rotating plate  57  is making normal rotation or reverse rotation, i.e., whether the rotor  19  is making normal rotation or reverse rotation. Also, one of the sensors  59   a ,  59   b  is used to detect whether the rotor  19  is rotating or not. 
     Next, a control block diagram in  FIG. 13  of the medicine dispenser  11  will be explained. The control circuit  61  is provided by a microcomputer, with a memory circuit  65  which includes a RAM and a ROM. The memory circuit  65  stores programs for performing various control operations to be described below. 
     Specifically, the control circuit  61  controls the drive motor  38  of the medicine feeder  13  via a drive circuit  62 , and controls the switching motor  39  via a drive circuit  63 . Also, detection signals from the tablet counting sensor  25  and the rotor-rotation detection sensor  58  which are provided in the medicine feeder  13  are inputted to the control circuit  61 . 
     The dispenser  11  is provided with a display device  64  for indication of errors such as a clogging error and a missing tablet error. These error indications are made in accordance with signals from the control circuit  61 . The control circuit  61  works with an input device  66  which may be provided by a personal computer for example, and a timer  67 . Through the input device  66 , prescribing information, etc., is entered, and the information is stored in the memory circuit  65 . 
     Next, control operations by the control circuit  61  will be described based on flowcharts in  FIG. 14  through  FIG. 16 . 
     Upon commencement of a tablet dispensing operation, Step (hereinafter abbreviated simply as “S”)  1  starts the drive motor  38 , the rotor-rotation detection sensor  58 , the tablet counting sensor  25  and the timer  67 . If S 2  determines that the rotor  19  is in normal rotation (YES), S 3  checks to see if the rotor  19  is rotating. If rotating (YES), S 4  determines whether or not a tablet has been dropped, based on a signal obtained from the tablet counting sensor  25 . 
     If the tablet has been dropped (YES), S 5  continues counting of the tablets until S 6  determines that the quantity of the tablets has reached a quantity which is pre-set as prescribing information. When the count has reached the pre-set number (YES), S 7  stops the tablet dispensing operation, makes a display which indicates completion of the tablet dispensing operation in the display device  64 , and then the process brings the tablet dispensing operation to an end. 
     If S 4  determines that a tablet has not been dropped (NO), S 10  starts time measurement, and the process keeps coming back to S 4  as long as S 11  determines that a period of n seconds has not elapsed (NO). After the lapse of the n seconds (YES), S 12  stops the operation. Then, S 13  makes an error display about a missing tablet, and then the process brings the operation to an end. 
     If S 2  determines that the rotor  19  is not in normal rotation (NO), the process branches off to S 14 , to see if the rotor  19  is rotating. If the rotor  19  is rotating (YES), the rotation is reverse rotation, so the process executes S 15  subroutine (see  FIG. 15  to be described later) to drive the rotor  19  in the normal rotation direction, and then returns to S 3 . 
     If S 14  determines that the rotor  19  is not rotating (NO), it indicates, for example, that a jammed tablet or other trouble at the start up of operation has disabled the rotor  19  from rotating. Therefore, S 16  is executed to start time measurement, and the process keeps coming back to S 14  as long as S 17  determines that a period of n seconds has not elapsed (NO). After the lapse of the time (YES), S 18  subroutine (see  FIG. 16  to be described later) is performed for driving the rotor  19  in reverse rotation direction as an attempt to clear the jammed tablet. 
     After S 18  subroutine has attempted the reverse driving, S 19  subroutine is executed to drive the rotor  19  in normal rotation direction. If S 20  determines that the rotor  19  is turning in the normal rotation direction (YES), it is determined that the jammed tablet has been cleared, and the process goes back to S 4 . Otherwise (NO), S 21  stops the operation, S 22  makes an error display about a jammed tablet, and then the process brings the operation to an end. 
     If S 3  determines that the rotor  19  is not rotating (NO), it indicates, for example, that a jammed tablet or other trouble during normal rotation of the rotor  19  in the dispensing operation has disabled the rotor  19  from rotating. Therefore, the process jumps to execute S 16  and the steps from S 17  through S 19  for driving the rotor  19  in the reverse rotating direction and then the normal rotating direction, as an attempt to clear the jammed tablet. After S 20  determines whether the rotor  19  is rotating in the normal rotation direction (YES), or not (NO), the process performs the operations, accordingly as described above. 
       FIG. 15  shows the subroutine for driving the rotor in the normal rotation direction: If S 101  determines that the drive motor  38  is in stoppage (YES), S 102  drives the switching motor  39 . If the drive motor  38  is not in stoppage (NO), S 103  stops the drive motor  38 . 
     In S 104 , the switching motor  39  is driven to switch the rotor  19  to rotate in the normal rotation direction. The switching motor  39  is stopped in S 105 , the drive motor  38  is driven in S 106 , and the rotor  19  is driven in the normal rotation direction, and then the process makes a return in S 107 . 
       FIG. 16  shows the subroutine for driving the rotor  19  in the reverse rotation direction: If S 201  determines that the drive motor  38  is in stoppage (YES), S 202  drives the switching motor  39 . If the drive motor  38  is not in stoppage (NO), S 203  stops the drive motor  38 . 
     In S 204 , the switching motor  39  is driven to switch the rotor  19  to rotate in the reverse rotation direction. The switching motor  39  is stopped in S 205 , and the drive motor  38  is driven in S 206 . As the drive motor  38  is driven, the rotor  19  is driven in the reverse rotation direction in S 207  and then time measurement is started in S 208 . S 209  checks if a period of n seconds has elapsed, and if the obtained answer is NO, the process goes back to S 206 . If the obtained answer is YES, S 210  drives the drive motor  38 , and then the process makes a return. 
     The medicine dispenser  11  according to the first embodiment is configured as described thus far. In its medicine feeder  13 , reverse rotation of the rotor  19  for clearing a jammed medicine is achieved by first stopping the drive motor  38 , and then driving the switching motor  39  thereby switching the power transmission path to the reverse-rotation transmission path  46 . Thereafter, the drive motor  38  is driven to make normal rotation, whereby driving power is transmitted to the rotor  19  via the reverse-rotation transmission path  46 , causing the rotor  19  to rotate in the reverse direction. As described, the arrangement is capable of rotating the rotor  19  in the reverse direction not by driving the drive motor  38  in a reverse direction but by driving it in the normal direction. Thus, the arrangement can reduce the burden on the drive motor  38 . 
     Also, as has been described, the arrangement provides, within the control circuit  61 , means for determining whether or not the rotor  19  is rotating (S 3  in  FIG. 14 ), based on signals from the rotor-rotation detection sensor  58 ; and means for determining whether or not the tablet dispensing operation is proceeding successfully (S 4  in  FIG. 14 ), based on signals from the tablet counting sensor  25 . Using these determination means, an error display is performed regarding a missing tablet (S 13  in  FIG. 14 ) if the rotor is rotating but a tablet has not been dispensed for a predetermined period of time (S 11  in  FIG. 11 ). The arrangement establishes differentiation between a jammed tablet and a missing tablet, thereby offering a reliable detection of a missing tablet in cases where a tablet is not dispensed. 
     Further, the arrangement provides a greater speed reduction ratio for drive power transmission via the reverse-rotation transmission path  46  than via the normal-rotation transmission path  45 . Thus, it is possible to apply a relatively greater torque when rotating the rotor  19  in reverse. This facilitates smooth clearing of a jammed tablet. 
     It should be noted here that a detection of an overcurrent to the drive motor  38  or a detection by the tablet counting sensor  25  of a no-tablet-dispensed event may be used as a basis for the determination that a tablet has jammed, which is then followed by the above-described switching operation for driving the rotor  19  in reverse. 
     These functions and advantages are also offered by the second embodiment which will be described next. 
     Second Embodiment 
     A medicine dispenser  11  shown in  FIG. 17  through  FIG. 22  according to the second embodiment is essentially the same as the first embodiment (see  FIG. 1 ) in its basic configuration. Also, a medicine feeder  13  includes a dispensing cassette  16  of the same configuration as in the previous embodiment (see  FIG. 2  through  FIG. 4 ). However, there are some differences in the internal structure of the drive unit  17 . 
     Specifically, as shown in  FIG. 17  and  FIG. 18 , the drive unit  17  according to the second embodiment has a drive motor  38 , and a switching solenoid  71  (hereinafter, simply called solenoid  71 ) as a switching actuator. A motor shaft  41  of a drive motor  38  is parallel with a plunger  72  of the solenoid  71 . Further, these two members are perpendicular to an output shaft  31 . 
     A worm gear  73  is mounted to the motor shaft  41 , and the worm gear  73  engages with a worm ring  74 , which is mounted rotatably to a case  75 . The worm ring  74  is a two-stage gear, which has a small-diameter wheel  74   b  engaged with the worm gear  73 , whereas a large-diameter wheel  74   a  engages with a switching gear  47 . The worm gear  73  has a left-hand helix. When the drive motor  38  makes normal rotation, the worm gear  73  on the motor shaft  41  makes normal rotation, and the worm ring  74  engaged thererwith makes normal rotation (see  FIG. 19 ). 
     The worm ring  74  has a support shaft  76 , which is supported by the case  75  (see  FIG. 18 ). With this worm ring  74  in between, two pivot arms  77 ,  77  have their respective upper end portions attached pivotably to the support shaft  76 . The switching gear  47  has a support shaft  78 , which has its two end portions attached rotatably to intermediate portions of the pivot arms  77 ,  77 . Also, one of the pivot arms  77  has its lower end portion movably connected with an end of an intermediate link  79  which is laid perpendicularly to the pivot arm, by a pin  80  (see  FIG. 17 ). 
     The intermediate link  79  has a rear end portion, which is connected movably to the plunger  72  of the solenoid  71  by a pin  81 . When the solenoid  71  is operated, the plunger  72  moves in a horizontal direction with movable joints provided by the two pins  80 ,  81 , pivoting the pivot arms  77 ,  77  to perform a switching operation by bringing the switching gear  47  into a normal-rotation transmission path  45  or into a reverse-rotation transmission path  46 . 
     As shown in  FIG. 19  and  FIG. 20 , the normal-rotation transmission path  45  in this case is constituted by four (even number of) gears, i.e., the worm ring  74  as a drive gear; the switching gear  47 ; a middle gear  48 ; and an output gear  44 . Like in the first embodiment, the output gear  44  is attached to the output shaft  31 . The switching gear  47  is a two-stage gear, which has a small-diameter wheel  47   b  engaged with the large-diameter wheel  74   a  of the worm ring  74 . Also, the switching gear  47  has its large-diameter wheel  47   a  engaged with the middle gear  48 . 
     As shown in  FIG. 21  and  FIG. 22 , the reverse-rotation transmission path  46  is constituted by five (odd number of) gears, i.e., the worm ring  74  as a drive gear; the switching gear  47 ; a first middle gear  49 ; a second middle gear  50 ; and the output gear  44 . Each of the first middle gear  49  and the second middle gear  50  is provided by a two-stage gear: The former has a large-diameter wheel  49   a  engaged with a large-diameter wheel  47   a  of the switching gear  47 ; and a small-diameter wheel  49   b  engaged with a large-diameter wheel  50   a  of the second middle gear  50 . The second middle gear  50  has a small-diameter wheel  50   b  engaged with the output gear  44 . 
       FIG. 18  shows axial positional relationship of the above-described gears: the two-stage worm ring  74  has its large-diameter wheel  74   a  in Layer “a” whereas its small-diameter wheel  74   b  is located across Layer “b” and Layer “c”. 
       FIG. 20  shows positional relationship in the normal-rotation transmission path  45 : The large-diameter wheel  47   a  of the switching gear  47  is in Layer “b”, and its small-diameter wheel  47   b  in Layer “a”. The small-diameter wheel  47   b  is in engagement with the large-diameter wheel  74   a  of the worm ring  74 . The middle gear  48  is in Layer “b” and is in engagement with the large-diameter wheel  47   a  of the switching gear  47 . The output gear  44  is in Layer “b” and in engagement with the middle gear  48 . 
       FIG. 22  shows positional relationship in the reverse-rotation transmission path  46 : The large-diameter wheel  49   a  of the first middle gear  49  is in Layer “b” (behind the large-diameter wheel  47   a  of the switching gear  47  in the Figure) whereas the small-diameter wheel  49   b  is in Layer “c”. The large-diameter wheel  49   a  is in engagement with the large-diameter wheel  47   a  of the switching gear  47 , in Layer “b”. The large-diameter wheel  50   a  of the second middle gear  50  is in Layer “c” whereas the small-diameter wheel  50   b  is in Layer “b”. The large-diameter wheel  50   a  is in engagement with the small-diameter wheel  49   b  of the first middle gear  49  whereas the small-diameter wheel  50   b  is in engagement with the output gear  44  in Layer “b”. The small-diameter wheel  50   b  of the second middle gear  50  has a smaller diameter than the output gear  44  for rotation at a predetermined speed reduction ratio. 
     A comparison between the normal-rotation transmission path  45  and the reverse-rotation transmission path  46  will reveal the following: After the switching gear  47 , the normal-rotation transmission path  45  has only one gear engagement between the middle gear  48  and the output gear  44  (see  FIG. 17 ), and their speed reduction ratio is relatively small. On the contrary, the reverse-rotation transmission path  46  has two gear engagements, i.e., one between the small-diameter wheel  49   b  of the first middle gear  49  and the large-diameter wheel  50   a  of the second middle gear  50 ; and the other between the small-diameter wheel  50   b  of the second middle gear  50  and the output gear  44 . The two speed-reduction engagements provide a relatively large reduction ratio. 
     The medicine dispenser according to the second embodiment is configured as described thus far. With the switching gear  47  switched to the normal-rotation transmission path  45  as shown in  FIG. 19 , the drive motor  38  gives normal rotation to the worm ring  74  via the worm gear  73 ; the rotation is transmitted via the normal-rotation transmission path  45 ; and the output shaft  31  makes reverse rotation. As shown in  FIG. 3 , the above-described operation causes the rotor  19  to make normal rotation in the dispensing cassette  16 , and a tablet is dispensed. 
     Also, as shown in  FIG. 21 , the solenoid  71  is activated to move the plunger  72 , the intermediate link  79  and the pivot arms  77 , to switch the switching gear  47  to the reverse-rotation transmission path  46 . The normal rotation of the drive motor  38  makes normal rotation of the worm ring  74 ; the rotation is transmitted via the reverse-rotation transmission path  46 ; and the output shaft  31  makes normal rotation. Thus, the rotor  19  rotates in the reverse direction in the dispensing cassette  16  as an attempt to clear a jammed tablet. 
     In the reverse rotation transmission after the reverse-rotation transmission path  46 , a greater speed reduction ratio is obtained, as described earlier, than in the normal rotation transmission, as well as a relatively greater reverse rotation torque concomitantly. 
     Other aspects, including the rotor-rotation detection sensor  58  (see  FIG. 18 ) provided on the output shaft  31 , are the same as in the first embodiment. Also, the control block diagram and the flowchart for this embodiment are the same as in  FIG. 13  through  FIG. 16 , differing only in that the “switching motor” is replaced by the “switching solenoid” 
     Third Embodiment 
       FIG. 23  shows a medicine feeder according to a third embodiment, which includes a drive unit  17  having a drive motor  38  and a switching motor  39 . Their motor shafts  41 ,  42  are perpendicular to each other, and a slide shaft  83  is provided in parallel to the motor shaft  41 . The slide shaft  83  is rotatable integrally with an output shaft  31  via a damper  84 . A coupling  32  is attached to a tip of the output shaft  31 . 
     Between the motor shaft  41  of the drive motor  38  and the output shaft  31 , a normal-rotation transmission path  45  and a reverse-rotation transmission path  46  are provided. The normal-rotation transmission path  45  is constituted by a drive gear  85  attached to the motor shaft  41 , and an output gear  86  engaged therewith. The output gear  86  is coaxial with the slide shaft  83 . The output gear  86  has a boss with an internal recess formed with a female spline  88  (see  FIG. 24A ) for engagement by a male spline  89  provided on the slide shaft  83 . 
     The reverse-rotation transmission path  46  is constituted by the above-described drive gear  85 , a middle gear  90  and an output gear  91 . The output gear  91  is coaxial with the slide shaft  83 . The output gear  91  has a boss with an internal recess formed with a female spline  88  (see  FIG. 24A ) for engagement by the above-described male spline  89  which is provided on the slide shaft  83 . The output gear  91  has a sufficiently greater diameter than the first middle gear  90 , so that a greater speed reduction ratio is obtained in this portion than in the normal-rotation transmission path  45 . 
     It should be noted here that desirably, the male spline  89  is tapered on its both end portions as shown in FIG.  24 B so that the male spline  89  can make smooth engagement with the female spline  88  upon a reciprocal movement of the slide shaft  83  over a predetermined stroke L. 
     The damper  84  is provided at a rear end of the output shaft  31 , with a spring  92  placed therein. The slide shaft  83  has its rear end inserted into the damper  84 , to press the spring  92 . A D-cut is provided in the slide shaft  83  where it is inserted into the damper  84 , so that the slide shaft  83  and the output shaft  31  can rotate integrally with each other while allowing sliding movement relative to each other. 
     The slide shaft  83  has a tip, and this tip is pressed by a pivot arm  93  which is moved by the switching motor  39 . As the pivot arm  93  pivots by a predetermined angle from a state drawn in solid lines in the  FIG. 23 , the slide shaft  83  is moved axially by a predetermined stroke L, disengaging the male spline  89  from the female spline  88  in the output gear  86 , and engaging it with the female spline  88  in the output gear  91 . 
     It should be noted here that the output shaft  31  is provided with the same rotor-rotation detection sensor  58  as in the first embodiment, although it is not illustrated in the drawings. 
     The third embodiment has been described thus far: When the switching motor  39  is in stoppage, the pivot arm  93  is in a retracted state as illustrated in solid lines in  FIG. 23 , and the male spline  89  of the slide shaft  83  is in engagement with the female spline  88  in the output gear  86 . 
     As the drive motor  38  makes normal rotation under this state, the rotating power is transmitted via the normal-rotation transmission path  45 , i.e., the drive gear  85  and the output gear  86  engaged therewith; and a clutch  87  provided by the female and male splines  88 ,  89 ; driving the slide shaft  83  and the output shaft  31  in the reverse rotation direction. In the dispensing cassette  16  (see  FIG. 3 ) which is connected via a coupling  32 , an input of the reverse rotation torque drives the rotor  19  in the normal rotation direction. 
     It should be noted here that in the above-described operation, the middle gear  90  and the output gear  91  move in association with the operation. However, their female spline  88  is not in engagement with the male spline  89 , so there is no transmission of power to the slide shaft  83 . 
     When the switching motor  39  is operated to move the pivot arm  93  to slide the slide shaft  83  by a predetermined stroke L, the male spline  89  is disengaged from the female spline  88  in the output gear  86 , and engaged with the female spline  88  of the second middle gear  91 . The movement of the slide shaft  83  is absorbed by the damper  84 , so there is no axial positional change in the output shaft  31 . 
     Upon the above-described switching, the normal-rotation drive power from the drive motor  38  is transmitted via the reverse-rotation transmission path  46 , to drive the slide shaft  83  and the output shaft  31  in the normal rotation direction. The normal rotation is transmitted via the coupling  32  to the dispensing cassette  16 , driving the rotor  19  in reverse. 
     Since a greater speed reduction ratio is obtained in this driving power transmission via the reverse-rotation transmission path  46  than via the normal-rotation transmission path  45 , the rotor  19  receives a relatively greater reverse rotation torque. 
     The drive unit described thus far according to the third embodiment is coupled with the dispensing cassette  16  to constitute the earlier-described medicine feeder  13  like in the first and second embodiments, and is mounted in the medicine dispenser  11 . A control block diagram and a flowchart for this embodiment are the same as in  FIG. 13  through  FIG. 16 . 
     Fourth Embodiment 
       FIG. 25  shows a drive unit  17  according to a fourth embodiment, which is essentially the same as in the third embodiment, with differences in its switcher. Specifically, the switcher in the present embodiment has an eccentric cam attached to a motor shaft  42  of a switching motor  39 . Also, a clutch plate  95  is attached to a slide shaft  83  between the output gear  86  of the normal-rotation transmission path  45  and the output gear  91  of the reverse-rotation transmission path  46 . 
     While the switching motor  39  is in stoppage, the eccentric cam  94  does not work on the slide shaft  83  as shown in the Figure. The clutch plate  95  is in engagement with an engagement projection  96  of the output gear  86 , so the power is transmitted via the slide shaft  83 , to drive the output shaft  31  in the reverse rotation direction. 
     As the switching motor  39  is driven, the eccentric cam  94  slides the slide shaft  83  by a predetermined stroke L. In this movement, the clutch plate  95  is disengaged from the output gear  86 , moved toward the output gear  91 , and engaged with the projection  96 , so that the power is now transmitted via the slide shaft  83  to drive the output shaft  31  in the normal rotation direction. 
     It should be noted here that the drive unit according to the fourth embodiment is also provided with a rotor-rotation detection sensor for the output shaft  31 , coupled with the dispensing cassette  16  like in the third embodiment to constitute the earlier-described medicine feeder  13 , which is mounted in the medicine dispenser  11 . A control block diagram and a flowchart for this embodiment are the same as those given in  FIG. 13  through  FIG. 16 . 
     LEGEND 
     
         
         
           
               11  Medicine dispenser 
               13  Medicine feeder 
               16  Dispensing cassette 
               17  Drive unit 
               18  Medicine storage 
               19  Rotor 
               25  Tablet counting sensor 
               26  Input shaft 
               31  Output shaft 
               38  Drive motor 
               39  Switching motor 
               41  Motor shaft 
               43  Drive gear 
               44  Output gear 
               45  Normal-rotation transmission path 
               46  Reverse-rotation transmission path 
               47  Switching gear 
               57  Rotating plate 
               58  Rotor-rotation detection sensor 
               61  Control circuit 
               62  Drive circuit 
               63  Drive circuit 
               71  Solenoid