Abstract:
A rotation detection device is provided in a motor roller of a conveying apparatus to detect changes in the rotation speed of the motor roller. When an object is moved from an upstream location of a conveyance path to the motor roller having the rotation detection device, the rotation detection device detects the presence of the object by measuring the slight variation in rotation speed of the motor roller. A control unit is provided to monitor the output signals from a plurality of rotation detection devices, arranged along the conveyance path. The control device independently adjusts the conveyance speeds of a plurality of independent conveyance portions along the conveyance path based upon these output signals. This system allows conveyance of a plurality of objects along the conveyance while avoiding one object from running into another object due to, for example, a delay at a particular point along the conveyance path.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a conveying apparatus which uses motor rollers to convey and detect an object being conveyed. 
     Conventional conveying apparatuses, such as, for example, accumulating conveyors, have a structure such that the conveying area is divided into a plurality of sections along the conveying path. When an object is conveyed onto a conveying section in the situation where another object temporarily rests in the conveying section located downstream from the conveying section, the object in the upstream conveying section is paused. Once to object in the downstream conveying section is moved out, conveyance of the object in the upstream conveying section is resumes. Thus, a plurality of objects are conveyed in succession while being prevented from coming onto contact with one another. 
     In order to detect objects that are being conveyed, such a conveying apparatus typically includes a detecting means which may use a photoelectric switch or include a switch that can be turned on or off by a rotatable free roller which is being pushed down by the weight of an object. Other conventional conveying apparatus have a structure such that an encoder incorporated in a rotatable free roller is caused to output pulses by the free roller that turns in the manner of slave rotation when an object passes thereon. 
     In order to detect objects, however, conventional conveying apparatuses require a special detecting means that is provided separately from the conveying device. Providing such a separate detecting means increases the number of parts and complicates the structure. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a conveying apparatus which overcomes the problem. 
     It is a further object of the present invention is to provide a conveying apparatus which is capable of carrying and detecting objects while having a simple structure that does not necessitate a special detecting means, but merely uses motor rollers. 
     Briefly stated, the present invention provides a rotation detection device in a motor roller of a conveying apparatus to detect changes in the rotation speed of the motor roller. When an object is moved from an upstream location of a conveyance path to the motor roller having the rotation detection device, the rotation detection device detects the presence of the object by measuring the slight variation in rotation speed of the motor roller. A control unit is provided to monitor the output signals from a plurality of rotation detection devices, arranged along the conveyance path. The control device independently adjusts the conveyance speeds of a plurality of independent conveyance portions along the conveyance path based upon these output signals. This system allows conveyance of a plurality of objects along the conveyance while avoiding one object from running into another object due to, for example, a delay at a particular point along the conveyance path. 
     According to an embodiment of the present invention, there is provided a conveying apparatus, comprising: at least a first motor roller and a second motor roller; at least a first motor unit and a second motor unit; the first motor roller and the second motor roller each having a roller portion rotated by the first motor unit and the second motor unit, respectively; the first motor roller and the second motor roller providing conveying means for conveying an object along a conveyance path; a rotation detecting unit providing a rotation detection signal by detecting rotation of each of the roller portion; and control means for monitoring the rotation detection signal, thereby detecting a position of the object along the conveyance path. 
     According to another embodiment of the present invention, there is provided a conveying apparatus, comprising: a conveyance path; the conveyance path being divided into a plurality of independent conveying sections; conveyance means for moving objects along the conveyance path; detection means for detecting the presence of the object at one of the plurality of independent conveying sections of the conveyance path; control means for adjusting a speed of each of the plurality of independent conveying sections, whereby the objects are prevented from contacting each other; and the detection means includes measuring means for measuring the conveying speed of each of said plurality of independent conveying sections, thereby detecting a slight variation in the conveying speed when one of the objects moves into one of the plurality of independent conveying sections. 
     A conveying apparatus according to an embodiment of the present invention includes motor rollers, each of which is provided with a motor unit, a roller portion adapted to be rotated by said motor unit, and a rotation detecting unit for detecting rotation of the roller portion and outputting signals representing results of detection. A conveying device is adapted to carry objects by using the motor rollers. A control means is adapted to monitor detection signals output from the rotation detecting units of said motor rollers so as to detect objects based on changes in rotation of the roller portions. 
     With the configuration as above, the conveying apparatus makes use of the rotation detecting units that is incorporated in each motor roller for the purpose of control of its speed in such a way that the apparatus monitors detection signals output from the rotation detecting unit of the corresponding motor roller. These rotation detecting units detect an object based on change in rotation of the roller portion, which occurs when the object reaches the roller portion. 
     A conveying apparatus according to a feature of the present invention has the control means adapted to detect an object by monitoring detection signals output from the corresponding rotation detecting unit while rotating the corresponding motor roller at a constant speed. 
     As described above, the conveying apparatus detects an object by monitoring detection signals output from the corresponding rotation detecting unit while rotating the corresponding motor roller at a constant speed. Even if a reduction gear element is incorporated in each motor roller, arrival of an object causes change of rotation of the roller a portion more easily than when the motor roller is at a standstill. Therefore, the conveying apparatus ensures reliable detection of an object even if the object is light in weight. 
     A conveying apparatus according to another feature of the present invention has the control means adapted to detect an object by monitoring detection signals output from the corresponding rotation detecting unit while rotating the corresponding motor roller at a detection speed that is lower than a given conveying speed at which objects are conveyed. 
     When detecting an object, the conveying apparatus monitors detection signals output from the corresponding rotation detecting unit while rotating the motor roller at a detection speed that is lower than a given, conveying speed at which objects are conveyed. As a result of this feature, an object that has been conveyed at a given conveying speed easily changes rotation of a roller portion when the object reaches the roller portion. Therefore, the conveying apparatus ensures reliable detection of an object even if the object is light in weight. 
     A conveying apparatus according to a further feature of the present invention has a control means adapted to either increase the rotation speed of the corresponding motor roller up to the conveying speed, or stop its rotation, when the control means has detected an object. 
     By controlling a motor roller so as to either increase its rotation speed up to the conveying speed or stop its rotation upon detection of an object, the conveying apparatus either moves or stops the detected object. 
     A conveying apparatus according to another feature of the present invention is a conveying apparatus wherein the conveying device is provided with a plurality of conveying sections arranged along the conveying path along which objects are conveyed. Each conveying section has at least one motor roller. The control means of the apparatus is adapted to rotate the motor roller of a conveying section at the detection speed when an object rests in the conveying section that is located downstream from said conveying section. When another object is detected at the former conveying section, i.e. the upstream conveying section, the conveying apparatus temporarily stops the object in the upstream conveying section, and moves the object in the upstream conveying section after the object in the downstream conveying section is moved out of the downstream conveying section. 
     By thus rotating the motor roller of a conveying section at the detection speed when an object rests in the conveying section that is located downstream from the conveying section, and, when another object is detected at the upstream conveying section, temporarily stopping the object in the upstream conveying section, and moving the object in the upstream conveying section downstream after the object in the downstream conveying section is moved out of the downstream conveying section, the conveying apparatus performs accumulation of objects that are being conveyed. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system block diagram of a conveying apparatus according to an embodiment of the present invention. 
     FIG.  2 ( a ) is a top view of the conveying apparatus according to the present invention. 
     FIG.  2 ( b ) is a side section of the conveying apparatus of FIG.  2 ( a ). 
     FIG. 3 is a sectional view of a motor roller of the conveying apparatus of the present invention. 
     FIG. 4 is a side view of the magnet of the motor roller of FIG.  3 . 
     FIG. 5 is an explanatory drawing for explaining how the conveying apparatus of the present invention detects conveyed objects. 
     FIG.  6 ( a ) is a waveform chart of pulses output from a rotation detecting unit before an object reaches a motor roller. 
     FIG.  6 ( b ) is a waveform chart of pulses output from the rotation detecting unit when the object reaches the motor roller. 
     FIGS.  7 ( a ) and ( b ) are explanatory drawings for illustrating a procedure of accumulation according to an embodiment of the present invention. 
     FIGS.  8 ( a ), ( b ) and ( c ) are explanatory drawings for illustrating the procedure of start-up after accumulation is conducted as shown in FIG.  7 . 
     FIGS.  9 ( a ), ( b ) and ( c ) are explanatory drawings for illustrating another procedure of accumulation according to an alternate embodiment of the present invention. 
     FIGS.  10 ( a ) and ( b ) are explanatory drawings for illustrating the procedure of start-up after accumulation is conducted as shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS.  2 ( a ) and  2 ( b ), a roller conveyor type accumulating conveyor  11 , serves as the conveying device to convey objects. A conveyor frame  12  includes a pair of side frames  13  and a plurality of laterally extending connecting members (not shown) for connecting side frames  13  to one another. Side frames  13  are parallel to each other and extend along the conveying path F along which objects are conveyed. Thus, side frames  13  form the two sides of conveying path F. 
     A plurality of motor rollers  14  and free rollers  15  are disposed between the two side frames  13  that form the two lateral sides of conveyor frame  12 . Motor rollers  14  and free rollers  15  are arranged side by side along conveying path F to form a conveying surface  16  to carry objects. 
     Conveying surface  16  is divided into a plurality of conveying sections that are arranged side by side along conveying path F in such a manner that each conveying section is provided with at least one motor roller  14  and a plurality of free rollers  15  (two free rollers  15  in case of the present embodiment). In other words, a plurality of motor rollers  14  are arranged at a given pitch (at every third roller in case of the present embodiment), with a plurality of free rollers  15  (two free rollers  15  in case of the present embodiment) disposed between each motor roller  14  and its adjacent motor roller  14 . 
     Referring to FIG. 3, each motor roller  14  comprises a cylindrical roller portion  21 , shaft portions  22  and  23 , a motor unit  24 , a reduction gear element  25  and a rotation detecting unit  26 . Shaft portions  22  and  23  respectively project from the two opposing ends of the roller portion  21 , supporting roller portion  21  in such a manner that roller portion  21  easily rotates around shaft portions  22  and  23 . Motor unit  24  is disposed in roller portion  21  and attaches to one of the shaft portions, i.e. shaft portion  22 . Reduction gear element  25  serves to transmit the rotational driving force of motor unit  24  to roller portion  21 . Rotation detecting unit  26  is adapted to detect rotation of roller portion  21 , in other words rotation of motor unit  24 , and output signals representing results of detection. 
     Roller portion  21  is rotatably supported by shaft portion  22  at two locations, i.e. one of the two lateral ends of roller portion  21  and a location near the other end, with bearings  27  and  28  disposed between shaft portion  22  and the two locations. Roller portion  21  is also rotatably supported at the other end by means of the other shaft portion, i.e. shaft portion  23 . 
     Shaft portions  22  and  23  are spaced apart and aligned along the axis of roller portion  21  in such a manner as to be coaxial with roller portion  21 . Shaft portion  22  is a hollow cylinder defining a wiring space (not shown), which is adapted to contain a wiring. The end that projects from roller portion  21  has a mounting portion  30 , at which shaft portion  22  is fastened to the adjacent side frame  13  so that shaft portion  22  is prevented from rotating. Shaft portion  23  is capable of sliding on a bearing  29  so as to move back and forth along the axial direction between the location where shaft portion  23  projects from the end of roller portion  21  and the location where the principal part of shaft portion  23  is inside roller portion  21 . A spring  32 , disposed between shaft portion  23  and a spring receiver  31 , which is located closer to roller portion  21  than is shaft portion  23 , constantly pushes shaft portion  23  so as to hold shaft portion  23  at the position where it projects from roller portion  21 . The end of shaft portion  23  that projects from roller portion  21  has a mounting portion  33 , at which shaft portion  23  is fastened to the adjacent side frame  13  so that shaft portion  23  is prevented from rotating. Motor roller  14  is easily mounted between the two side frames  13  by attaching the mounting portion of one of the shaft portions, e.g. mounting portion  30  of shaft portion  22 , to one of the side frames  13  from inside, and, thereafter, bringing the other end of roller portion  21  into the interior of the other side frame  13  in the state where the other shaft portion  23  is retracted inside the roller portion  21 , and then allowing the mounting portion  33  to project and connecting it to the side frame  13  from inside. 
     Motor unit  24  is preferably a dc motor having a stator  34 , a cylindrical rotor  35  disposed around stator  34 , and bearings  36 . Stator  34  is disposed at the approximate center of roller portion  21  and affixed to shaft portion  22 . Rotor  35  is rotatably supported at both ends by shaft portion  22 , with a bearing  36  disposed between each end of rotor  35  and shaft portion  22 . Stator  34  has a stator core and a stator winding. A lead wire  34   a  connected to the stator winding passes through the inside of shaft portion  22  and is drawn out of the shaft portion. 
     Reduction gear element  25  serves to reduce the torque of rotor  35  and transmits the reduced torque to roller portion  21 . Reduction gear element  25 , having an internal gear  37   a  and a planet gear mechanism  37   b,  has a structure such that the torque of rotor  35  is reduced and transmitted through planet gear mechanism  37   b  to internal gear  37   a,  which is attached to the inner cylindrical surface of roller portion  21 . 
     Rotation detecting unit  26  is comprised of a hole sensor having a ring-shaped magnet  38  and a hole element  39  disposed near magnet  38 . Magnet  38  is adapted to be coaxially mounted around rotor  35 , while hole element  39  is attached to shaft portion  22  in such a manner as to face magnet  38 . A lead wire, connecting to hole element  39  and passing through the inside of shaft portion  22 , is drawn out of the shaft portion. 
     Referring to FIG. 4, magnet  38  is polarized such that south poles and north poles are alternately arranged in a circle at 90° intervals. 
     Referring back to FIG. 3, rotation detecting unit  26  has a configuration such that one turn of rotor  35  causes two pulses to be output from hole element  39 . In the case where reduction gear element  25  has a reduction ratio of, for example, 1/43, one turn of roller portion  21  causes hole element  39  to output 86 pulses. 
     Each free roller  15  is similar to each motor roller  14  in its outer shape. Each free roller  15  has a cylindrical roller portion and shaft portions that respectively project from the two opposing ends of the roller portion so as to support the roller portion. A bearing is positioned between each shaft portion and the roller portion in such a manner as to permit the roller portion to easily rotate. 
     Referring to FIG. 1, a control means  41  controls accumulation performed by accumulating conveyor  11 . Control means  41  is adapted to adjust and control rotation speed of roller portion  21  by controlling the drive of motor unit  24  of each motor roller  14 . Control means  41  receives detection signals output from rotation detecting unit  26  with rotation of motor unit  24 . 
     Control means  41  has a function of monitoring detection signals output from rotation detecting unit  26  of each motor roller  14  and detecting a conveyed object based on changes in rotation, i.e. load changes, of roller portion  21 . To be more specific, when detecting an object that is being conveyed, control means  41  monitors detection signals output from rotation detecting unit  26  while rotating motor roller  14  at a constant speed, i.e. at a detection speed that is lower than a given conveying speed (normal speed) at which an object or objects are carried. The aforementioned detection speed and conveying speed will hereinafter be referred to as the low speed and the high speed respectively. Other functions of control means  41  include an accumulation function for rotating motor roller  14  of a conveying section when objects on a conveying section located downstream from said conveying section are at a standstill, temporarily stopping the objects on the former conveying section, i.e. the conveying section at the upstream side, when such objects are detected, and moving the objects in the upstream conveying section at the high speed when said other objects are moved out of the downstream conveying section. 
     Referring to FIGS. 5,  6 ( a ) and  6 ( b ), motor roller  14  of a conveying section A 1  is at a standstill so that an object M 1  thereon is not moving. When detecting an object M 2  that is being conveyed along conveying path F towards conveying section A 2 , located directly upstream from conveying section A 1  in the state described above, control means  41  rotates motor roller  14  of conveying section A 2  at the low speed. Throughout the period when motor roller  14  of conveying section A 2  rotates at the low speed, rotation detecting unit  26  of motor roller  14  outputs pulses at given intervals S 1 , e.g. 42 msec., as shown in FIG.  6 ( a ). 
     When motor roller  14  of conveying section A 3  at the upstream side rotates at the high speed and moves object M 2  rapidly toward conveying section A 2 , object M 2  reaches conveying section A 2  at a speed higher than the circumferential speed of motor roller  14  of conveying section A 2 , which is currently turning at the detection speed. Therefore, when object M 2  comes into contact with motor roller  14  of conveying section A 2 , the rotation speed of motor roller  14  is temporarily increased. At that time, each interval S 2 , of the pulses output from rotation detecting unit  26  of motor roller  14  that is rotating at the low speed becomes shorter than the aforementioned pulse interval S 1 . For example, the pulse interval S 2  may be 40 msec. in case of the present embodiment. 
     When generation of pulse interval S 2  that is shorter than pulse interval S 1  is detected, control means  41  judges that object M 2  has reached conveying section A 2  and accordingly halts the rotation of motor roller  14  of conveying section A 2  in order to stop the movement of object M 2 . 
     As described above, an object is detected by monitoring detection signals output from rotation detecting unit  26  of the corresponding motor roller  14  in order to detect a rotational change that is to occur at roller portion  21  when the object reaches the roller portion. By thus using rotation detecting unit  26  incorporated in each motor roller  14  for the purpose of controlling its speed, the embodiment described above is capable of carrying and detecting objects while having a simple structure that does not necessitate a special detecting means, but rather merely requires use of motor rollers  14 . 
     When detecting an object, this embodiment of the present invention calls for monitoring detection signals output from the corresponding rotation detecting unit  26  while rotating motor roller  14  at the detection speed that is lower than the conveying speed or the high speed, at which the object is conveyed. As it makes rotation of roller portion  21  easier to change when the object conveyed at the high speed reaches roller portion  21 , this feature ensures the reliable detection even if the object to be detected is light in weight. 
     In case an object to be detected is light in weight, it is impossible to detect it while motor roller  14  is at a standstill. Since reduction gear element  15  is disposed between motor unit  24  and roller portion  21 , a light object that has reached motor roller  14  merely slips on roller portion  21  instead of rotating the roller portion and, therefore, make its detection impossible. There may be various ways to allow roller portion  21  to rotate when an object reaches roller portion  21 . For example, motor roller  14  may incorporate a clutch that is adapted to turn on or off the driving system of motor unit  24  and roller portion  21 . However, inclusion of a clutch complicates both the structure and control of the apparatus and increases production costs. As a means to solve this problem, the present invention is adapted to detect an object by monitoring detection signals output from the corresponding rotation detecting unit  26  while rotating its motor roller  14  at the detection speed, which is lower than the high conveying speed at which the object is being conveyed. As it makes rotation of roller portion  21  easier to change when the object conveyed at the high speed reaches roller portion  21 , it ensures the reliable detection even if the object to be detected is light in weight. In other words, by actively rotating roller portion  21 , which is already rotating against dynamic friction instead of using static friction, the embodiment allows however small force of a lightweight object to easily change the rotation of roller portion  21 , thereby ensuring the reliable detection of the object. 
     Next, the accumulation function of control means  41  is explained hereunder. 
     Referring to FIGS.  7 ( a ) and  7 ( b ), the process of accumulation is explained. As an example, reference is made to a case where accumulating conveyor  11  is provided with a plurality of conveying sections, for example conveying sections A 1  through A 5 , which are arranged in the ascending order from the downstream side along conveying path F. During the time that the processing unit at the downstream side of accumulating conveyor  11  outputs accumulation command signals, motor roller  14  of conveying section A 1  at the downstream-most side is at a standstill so that object M 1 , too, is paused. In this state, either all motor rollers  14  of conveying sections A 2 -A 5  at the upstream side keep rotating at the low speed, or motor rollers  14  of conveying section A 2  and conveying section A 5 , which is at the upstream-most side, are rotated at the low speed, while motor rollers  14  of conveying sections A 3  and A 4  are at a standstill. 
     When arrival of object M 2  is detected at conveying section A 5 , located at the upstream-most side, motor rollers  14  of conveying sections A 3  through A 5  are rotated at the high speed to move object M 2  downstream, while motor roller  14  of conveying section A 2  is rotated at the low speed to prepare for arrival of object M 2  (the state shown in FIG.  7 ( a )). 
     When arrival of object M 2  is detected at conveying section A 2 , rotation of motor rollers  14  is halted to brake object M 2 , while motor rollers  14  of conveying section A 3 , which is located at the upstream side of conveying section A 2 , and conveying section A 5  are rotated at the low speed to prepare for arrival of an object that will follow. This state is shown in FIG.  7 ( b ). Meanwhile, motor roller  14  of conveying section A 4  maintains its high-speed rotation. However, after the elapse of a given period of time, the rotation speed of motor roller  14  is reduced or halted. 
     By thus rotating motor roller  14  of the conveying section located immediately upstream from the conveying section on which an object rests, the conveyor of the present invention is prepares the upstream conveying section for arrival of a succeeding object. Upon arrival of the succeeding objects, the conveyor halts rotation of this motor roller  14  to stop the object. The apparatus according to this embodiment of the present invention makes a plurality of objects carried on accumulating conveyor  11  remain on the conveyor without bringing them into contact with one another. 
     Referring to FIGS.  8 ( a ),  8 ( b ), and  8 ( c ), the process of post-accumulation start-up is described. As an example, reference is made to a case where objects M 1  through M 4  rest in conveying sections A 1  through A 4 , respectively, of accumulating conveyor  11 . When the processing unit at the downstream side of accumulating conveyor  11  outputs clearing command signals in this situation, motor roller  14  of conveying section A 1  at the downstream most side is rotated at the high speed so that object M 1  in conveying section A 1  moves downstream at the high speed and discharges out of the conveying section (the state shown in FIG.  8 ( a )). 
     When the processing unit at the downstream side of accumulating conveyor  11  detects object M 1  that has been carried out of conveying section A 1 , the apparatus rotates motor roller  14  of conveying section A 2  at the high speed. This carries object M 2  in conveying section A 2  downstream at the high speed and discharges it out of the conveying section, while rotating motor roller  14  of conveying section A 1  at the low speed (the state shown in FIG.  8 ( b )). 
     In case the processing unit at the downstream side of accumulating conveyor  11  is outputting accumulation command signals, when the discharge of object M 2  from conveying section A 2  is detected at conveying section A 1 , motor roller  14  of conveying section A 1  is halted so that object M 2  comes to a standstill in conveying section A 1 . In case there is an outstanding clearing command signal, the apparatus rotates motor roller  14  of conveying section A 1  at the high speed to move object M 2  in conveying section A 1  downstream at the high speed to discharge it out of the conveying section. Furthermore, the apparatus rotates motor roller  14  of conveying section A 3  at the high speed, thereby carrying object M 3  in conveying section A 3  downstream at the high speed to discharge it out of conveying section A 3  while rotating motor roller  14  of conveying section A 2  at the low speed (the state shown in FIG.  8 ( c )). 
     As described above, when an object has been carried out of a conveying section, motor roller  14  of said conveying section is rotated at the low speed to prepare for arrival of another object from the upstream side. This occurs while motor roller  14  of the conveying section located upstream from said first conveying section is rotated at the high speed so that the object is carried downstream and moved out of the conveying section. The apparatus thus discharges a plurality of objects on accumulating conveyor  11  out of the conveyor without bringing them into contact with one another. 
     Next, the accumulation function of control means  41 , according to another embodiment of the present invention, is explained. 
     Referring to FIGS.  9 ( a ),  9 ( b ), and  9 ( c ), when handling objects SH 1  and SH 2 , which are shorter in the dimension parallel to conveying path F, or objects L 1  and L 2 , which are longer in the dimension parallel to conveying path F, as shown in FIG.  9 ( a ), the pitch (accumulation pitch) of each conveying section is set at a length greater than the maximum possible length of each object, and each conveying section A 1  and A 2  is provided with a plurality of motor rollers  14 . In case of the present embodiment, each conveying section includes two motor rollers  14 , of which the one at the downstream side serves as the master roller, while the one at the upstream side serves as the slave roller. Because of the slave motor, sufficient force for carrying an object is always ensured, even when handling shorter objects SH 1  and SH 2 . 
     In case there is an accumulation command signal output to the downstream conveying section A 1 , the apparatus rotates motor roller  14  at the downstream portion of conveying section A 1  at the low speed while rotating all motor rollers  14  located upstream from motor roller  14  of conveying section A 1  at the high speed, thereby conveying an object SH 1  or L 1  downstream at the high speed (the state shown in FIG.  9 ( b )). 
     When the object SH 1  or L 1  reaches motor roller  14  at the downstream portion of conveying section A 1  and is detected there, the apparatus halts rotation of all the motor rollers of conveying section A 1  to brake object SH 1  or L 1  so that the object stops inside of conveying section A 1 . Furthermore, the apparatus rotates motor roller  14  at the downstream portion of conveying section A 2 , which is located immediately upstream from conveying section A 1 , at the low speed to get conveying section A 2  ready for arrival of a succeeding object SH 1  or L 2  (the state shown in FIG.  9 (C)). 
     As described above, the apparatus rotates, at the low speed, motor roller  14  at the downstream portion of the conveying section to which an accumulation command signal has been sent. The apparatus rotates, at the high speed, motor rollers  14  located upstream from the downstream motor roller  14 , thereby getting them ready to receive a succeeding object. When an object arrives, all motor rollers  14  of the conveying section are halted so that a single object rests within a single conveying section. Thus, the apparatus according to this embodiment of the present invention makes objects that are of various types and lengths and are being carried on accumulating conveyor  11  remain on the conveyor without bringing them into contact with one another. 
     Referring now to FIG. 10, the process of post-accumulation start-up is described. As an example, reference is made to a case where objects L 1  and L 2  rest in conveying sections A 1  and A 2 , respectively, of accumulating conveyor  11 . When the processing unit at the downstream side of accumulating conveyor  11  outputs clearing command signals in this situation, all motor rollers  14  in conveying section A 1 , located at the downstream-most side, rotate at the high speed so that object L 1  in conveying section A 1  moves downstream at the high speed and is discharged out of the conveying section A 1  (the state as shown in FIG.  10 ( a )). 
     When the processing unit at the downstream side of accumulating conveyor  11  detects object L 1  has been carried out of conveying section A 1 , the apparatus rotates motor roller  14  in the upstream portion of conveying section A 1  and all motor rollers  14  in conveying section A 2  at the high speed, thereby carrying object L 2  in conveying section A 2  downstream at the high speed and discharging it out of the conveying section, while rotating motor roller  14  in the downstream portion of conveying section A 1  at the low speed (the state shown in FIG.  10 ( b )). 
     In case the processing unit at the downstream side of accumulating conveyor  11  is outputting accumulation command signals when object L 2  discharged from conveying section A 2  is detected at conveying section A 1 , all motor rollers  14  in conveying section A 1  are halted so that object L 2  rests in conveying section A 1 . In case there is an outstanding clearing command signal, the apparatus rotates all motor rollers  14  in conveying section A 1  at the high speed to move object L 2 , in conveying section A 1 , downstream at the high speed to discharge it out of the conveying section. 
     As described above, when object L 1  has been carried out of a conveying section by means of high speed rotation of all motor rollers  14  in conveying section A 1 , the apparatus rotates motor roller  14  in the downstream portion of conveying section A 1  at the low speed and rotate motor roller  14  in the upstream portion at the high speed, thereby getting conveying section A 1  ready for arrival of object L 2  from the upstream side. Meanwhile, all motor rollers  14  of conveying section A 2 , located upstream from conveying section A 1 , rotate at the high speed so that object L 2  is carried downstream and moved out of the conveying section. The apparatus thus discharges objects of a plurality of types having different lengths on accumulating conveyor  11  out of the conveyor in succession without bringing them into contact with one another. 
     As described above, each motor roller  14  has the function of detecting an object, the function of carrying an object, and the function of stopping an object. Therefore, by merely using motor rollers  14 , accumulating conveyor  11  has a simple structure. 
     When carrying a heavy object, it is not always necessary to rotate motor roller  14  intended for detection of arrival of the object at the detection speed that is lower than the conveying speed. Detection signals output from rotation detecting unit  26  may be monitored while motor roller  14  at the constant conveying speed. Even if motor roller  14  intended for detection of arrival of the object is at a standstill, an object can still be detected, provided that the object is heavy enough to rotate roller portion  21  upon its arrival. 
     Although arrival of an object is detected by use of motor roller  14  according to the embodiment described above, discharge of an object can be detected by using a structure that calls for monitoring detection signals output from the proper rotation detecting unit  26  while rotating the corresponding motor roller  14  at a constant conveying speed. To be more specific, when an object becomes detached from motor roller  14 , the motor roller  14  is relieved of the load, and its rotation speed is momentarily increased. By watching for this change in rotation speed and making judgement based on this change, the apparatus is capable of detecting the discharge of the object. 
     Furthermore, the same effect and function is obtained by using an encoder as rotation detecting unit  26  of motor roller  14  instead of a hole sensor. 
     Using a dc motor for motor unit  24  of motor roller  14  ensures precise control of rotation speed and other characteristics. However, similar effect and function can be obtained by using an ac motor. 
     The conveying device used for the invention is not limited to a roller conveyor type accumulating conveyor the invention is also applicable to a belt conveyor type accumulating conveyor. In this case, the belt of each conveying section has to be rotated by at least one motor roller  14 . 
     According to the structure of an embodiment of a conveying apparatus of the present invention, an object is detected by monitoring detection signals output from the rotation detecting unit of the corresponding motor roller in order to detect change in rotation of the roller portion. This change occurs when the object reaches the roller portion. By thus using a rotation detecting unit that is incorporated in each motor roller for the purpose of control of its speed, the conveying apparatus is capable of carrying and detecting objects while having a simple structure that does not necessitate a special detecting means but merely requires use of the motor rollers. 
     When detecting an object, a conveying apparatus according to the present invention monitors detection signals output from the corresponding rotation detecting unit while rotating the motor roller at a constant speed. As a result of this feature, even if a reduction gear element is incorporated in each motor roller, arrival of an object causes change of rotation of the roller portion more easily than when the motor roller is at a standstill. Therefore, the conveying apparatus ensures reliable detection of an object, even if the object is light in weight. 
     When detecting an object, a conveying apparatus, according to a feature of the present invention, monitors detection signals output from the corresponding rotation detecting unit while rotating the motor roller at a detection speed that is lower than a given conveying speed at which objects are conveyed. As a result of this feature, an object that has been conveyed at a given conveying speed easily changes rotation of a roller portion when the object reaches the roller portion. Therefore, the conveying apparatus of the present invention ensures reliable detection of an object even if the object is light in weight. 
     When the conveying apparatus has detected an object, the apparatus controls rotation of the corresponding motor roller so as to either increase its speed up to the conveying speed or stop its rotation. Therefore, the conveying apparatus ensures reliable control to move or stop objects during the process of their conveyance. 
     The conveying apparatus, according to another feature of the present invention, calls for rotating the motor roller of a conveying section at the detection speed when an object is at a standstill in the conveying section that is located downstream from said conveying section. When another object is detected at the upstream conveying section, the apparatus temporarily stops the object in the upstream conveying section, and moves the object in the upstream conveying section after the object in the downstream conveying section is moved out of the downstream conveying section. Therefore, the conveying apparatus ensures reliable accumulation of objects that are being conveyed. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.