Abstract:
According to an aspect of an embodiment, there is provided a part-delivery apparatus which transports a part to a designated part-delivery position by drawing the part onto a head by suction pressure at a designated part-suction position, and which releases the part at the part-delivery position by stopping application of the suction pressure. The apparatus includes: a compliance mechanism for allowing movement of the head in a horizontal plane; an upper-side positioning unit for positioning the head in the part-suction position by responding to an upward movement of the head; and a lower-side positioning unit for positioning the head in the part-delivery position by responding to the downward movement of the head.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present art relates to an apparatus and method for delivering a part to a designated position by holding it on a head by suction pressure. 
         [0003]    2. Description of the Related Art 
         [0004]    An apparatus that utilizes pneumatic pressure is used to deliver a part to a part pallet or the like. Such a part-delivery apparatus transports a part by holding it by the tip of a head of a device by drawing air using an ejector, and places the part onto a pallet or the like by stopping the drawing of the air at a designated position on the pallet or the like. 
         [0005]    It is also known to use a feeder as an apparatus for successively feeding parts in an orderly aligned manner. The parts from the feeder are taken one by one by an operator and arranged on a tray to match the product shape, and then the parts are transported by being held by the heads of the part-delivery apparatus. 
         [0006]    The parts successively received from the feeder in an orderly aligned manner are held onto the heads at the receiving positions and transported in an orderly arranged condition in order to save the operator the trouble of arranging the parts on the tray. However, if the parts placed on a part pallet or the like are not arranged orderly there arises a need to correct the part-delivery positions effected by the heads. To accomplish this, the head unit must be equipped with a complex, high-cost mechanism for correcting the delivery positions. 
         [0007]    On the other hand, a pressure sensor for detecting a pressure change is mounted in a suction pipe passage in order to check the presence or absence of a part on the tip of the head (i.e., whether the part is held by the head or has been released). However, if part is not correctly detected for example, even when the ejector is activated to draw the part onto the head, but the part is actually held by the head, the pressure sensor may not turn on (indicating the fixedly held condition) because of air leakage. When the ejector is deactivated to release the part, and the pressure sensor has turned off (indicating the released condition), the part may remain held by the head. Since it is not possible to accurately detect whether the part has been released or not, a pusher for forcefully releasing the part is attached. 
         [0008]    Japanese Unexamined Patent Publication No. H02-156488, a prior art document related to the present art, discloses a magnetic head manufacturing method and apparatus in which positioning is achieved by a lowed driver hitting a tapered portion of a female screw (product side). Further, Japanese Unexamined Patent Publication No. H11-285925 discloses a part-mounting apparatus in which a suction nozzle having a detachable mounting head is equipped with an optical fiber bundle, which recognizes the mounting position of the part by examining a captured image transmitted through an optical guide path comprising the optical fiber bundle. 
         [0009]    On the other hand, Japanese Unexamined Patent Publication No. S59-134628 discloses an automatic screw tightening apparatus wherein when a screw chuck holding a screw moves down, the chamfer portion of the screw contacts the chamfer portion of the screw hole thereby correcting any positional displacement between them, and after the screw is tightened, the chuck moves upward and returns to the original position by the restoring force of a spring. Further, Japanese Unexamined Patent Publication No. H10-68759 discloses a suction-held object detecting apparatus for detecting a suction-held object by using a light-receiving sensor mounted within a transport arm and a light-emitting sensor mounted below a stage. 
       SUMMARY 
       [0010]    According to an aspect of an embodiment, there is provided a part-delivery apparatus which transports a part to a designated part-delivery position by drawing the part onto a head by suction pressure at a designated part-suction position, and which releases the part at the part-delivery position by stopping application of the suction pressure, the apparatus comprising: a compliance mechanism for allowing movement of the head in a horizontal plane; a first positioning unit for positioning the head in the part-suction position by responding to one of upward and downward movements of the head; and a second positioning unit for positioning the head in the part-delivery position by responding to the other one of the upward and downward movements of the head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The features and advantages of the present art will be apparent from the following description with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a perspective view showing the general construction of a part-delivery apparatus according to one embodiment of the present art; 
           [0013]      FIG. 2  is a perspective view showing the construction of a head assembly and its adjacent portions; 
           [0014]      FIG. 3  is a perspective view showing the head assembly and its adjacent portions when the head assembly is moved to the feeder position; 
           [0015]      FIG. 4  is a plan view showing part-delivery paths from feeders to a part pallet; 
           [0016]      FIG. 5  is a diagram explaining the positioning of the heads at part-suction positions; 
           [0017]      FIG. 6  is a diagram explaining the positioning of the heads at part-delivery positions; 
           [0018]      FIG. 7A  is a diagram explaining how the condition of a part is detected at a part-suction position; and 
           [0019]      FIG. 7B  is a diagram explaining how the condition of a part is detected at a part-delivery position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The embodiments of the present art will be described below with reference to the accompanying drawings.  FIG. 1  is a perspective view showing the general construction of a part-delivery apparatus according to one embodiment of the present art,  FIG. 2  is a perspective view showing the construction of a head assembly and its adjacent portions, and  FIG. 3  is a perspective view showing the head assembly and its adjacent portions when the head assembly is moved to the feeder position. The part-delivery apparatus shown is constructed so that screws as parts fed from two feeders  12  (respectively indicated by  12 A and  12 B) are held by suction onto six heads  20  (respectively indicated by  20 A,  20 B, . . . ,  20 F) and the six screws held on the respective heads are transported to a part pallet  60  and delivered to designated part-delivery positions on the part pallet  60 . 
         [0021]    Heads  20  are arranged in two rows in the X-axis direction and three rows in the Y-axis direction shown in  FIG. 1 . The mechanism including head assembly  20  is movable in the Y-axis direction. Head assembly  20  is constructed so that the six heads together can be moved up and down along the Z-axis direction. Further, as shown in  FIG. 2 , the mechanism including head assembly  20  is provided with six upper-side positioning units  42  (respectively indicated by  42 A,  42 B, . . . ,  42 F) and six lower-side positioning units  52  (respectively indicated by  52 A,  52 B, . . . ,  52 F) in corresponding relationship to the six heads  20 . 
         [0022]      FIG. 4  is a plan view showing part-delivery paths from the feeders  12 A and  12 B to part pallet  60  (as viewed from the direction opposing the Z axis in  FIG. 1 ). Parts (screws)  10  fed out of feeder  12 A in an orderly aligned manner are each loaded at a part-receiving position P 1 A directly into a cartridge  14 A serving as a loading device. As each part  10  is loaded, cartridge  14 A rotates 180 degrees thereby automatically transporting part  10  to a part-suction position P 2 A where corresponding head  20  can receive part  10  by suction. In like manner, parts  10  fed out of feeder  12 B are each loaded at a part-receiving position P 1 B into a cartridge  14 B and transported to a part-suction position P 2 B. 
         [0023]    In this way, since each part  10  fed out of feeder  12  is loaded into cartridge  14  ( 14 A or  14 B) and automatically transported to the position where corresponding head  20  can receive part  10  by suction, not only can the operator be saved the trouble of rearranging the parts on a tray, but also the need for such a tray can be eliminated. Besides, while cartridge  14  is automatically transporting one part  10  to the part-suction position, feeder  12  can feed out next part  10  in an orderly aligned manner, which serves to shorten the takt time. 
         [0024]    Then, head  20 A receives part  10  by suction at part-suction position P 2 A and transports it along the Y-axis direction for delivery to a part-delivery position P 3 A on pallet  60 . In like manner, heads  20 B,  20 C,  20 D,  20 E, and  20 F deliver parts  10  to corresponding part-delivery positions P 3 B, P 3 C, P 3 D, P 3 E, and P 3 F. 
         [0025]    Six heads  20  transport parts  10  by arranging them with spacing “a” along the X-axis direction and spacing “b” along the Y-axis direction as shown in  FIG. 4 . However, on pallet  60 , part-delivery position P 3 C is displaced in the X-axis direction and part-delivery position P 3 F in the Y-axis direction relative to the respective spacings so as to match the positions of the parts on the product. Therefore, in the part-delivery apparatus of the present art, heads  20  are not fixed, and a mechanism is provided that automatically accommodates the displacements between the part-suction positions and the part-delivery positions by positioning heads  20  by moving them up and down so as to pass through respective positioning units  42  and  52 . 
         [0026]      FIG. 5  is a diagram for explaining the positioning of heads  20  at the part-suction positions, and  FIG. 6  is a diagram for explaining the positioning of heads  20  at the part-delivery positions, both viewed from the direction opposing the Y axis. Each head  20  is provided at its center with a compliance mechanism  22  for allowing the movement of head  20  in a horizontal plane. Compliance mechanism  22  has a plurality of steel balls between two plates, and with these steel balls rolling, head  20  is allowed to move in the X- and Y-axis directions within a predefined range. 
         [0027]    As shown in  FIG. 5 , when taking part  10  from cartridge  14 , head  20  moves up passing through upper-side positioning unit  42  in contacting fashion and is thus positioned with respect to the part-suction position. After that, the ejector (not shown) connected to a part-suction coupling  26  is activated to draw part  10  onto head  20 . 
         [0028]    Head  20  with part  10  thus held thereon moves to a position above pallet  60 . Then, as shown in  FIG. 6 , head  20  moves down passing through lower-side positioning unit  52  in contacting fashion and is thus positioned with respect to part-delivery position. After that, the ejector (not shown) connected to part-suction coupling  26  is deactivated to deliver part  10  onto pallet  60 . 
         [0029]    In this way, when head  20  moves up and down passing through the respective positioning units, head  20  is fixed in a prescribed position by contacting the positioning units and thus positioned in place. Head  20  need only be made to contact each positioning unit so that head  20  can be fixed in a prescribed position for example, the positioning unit may be made to abut head  20  from four side or at a plurality of positions. Head  20  and its positioning units  42  and  52  are constructed so that upper-side positioning unit  42  and lower-side positioning unit  52  do not simultaneously act on head  20 . 
         [0030]    In the present embodiment, the heads are not fixed, but the positioning of each head is done by passing the head through the corresponding positioning units in contacting fashion accordingly. If there is a displacement between the position at which the part is drawn from the cartridge and the position at which the part is delivered to the pallet, there is no need to provide an actuator for correcting the head position. Furthermore, since by just moving the head in one axis direction (Z-axis direction), the positioning along the other two axis directions (X-axis and Y-axis directions) can be accomplished, the control load can be reduced. 
         [0031]    Further, since there is no need to rearrange the parts at some other location so as to match the spacing of the delivery positions, the takt time can be reduced. Moreover, if the product model is changed, such change can be handled by changing the mounting positions of the positioning units, which serves to significantly reduce cost. 
         [0032]      FIGS. 7A and 7B  are diagrams explaining how the condition of the part is detected at the part-suction and part-delivery positions, respectively. As shown in  FIGS. 7A and 7B , an optical fiber sensor  24  is mounted inside the tip of head  20  on which part  10  is held by suction, and the condition of part  10  is detected by detecting reflected light and determining whether or not part  10  is held on the head tip. 
         [0033]    The threshold value relating to the sensor amplifier output is changed between the part-suction position and the part-delivery position, and the condition of the part is detected at the respective positions. In other words, for the part-suction position, the threshold value relating to the sensor amplifier output is set so as to eliminate the possibility of erroneously determining that part  10  is not held on head  20  when part  10  is actually held on head  20  as shown in  FIG. 7A . On the other hand, for the part-delivery position, the threshold value relating to the sensor amplifier output is set so as to eliminate the possibility of erroneously determining that part  10  is still held on head  20  when part  10  has been delivered to pallet  60  as shown in  FIG. 7B . 
         [0034]    For the part-delivery position, two threshold values may be set in order to discriminate three conditions, i.e., the condition in which part  10  remains held on head  20 , the condition in which part  10  is placed on pallet  60 , and the condition in which part  10  is neither on the tip of head  20  nor on pallet  60 . 
         [0035]    By detecting the condition of part  10  using optical fiber sensor  24  as described above, an erroneous detection can be prevented from occurring due to pressure variations within head  20 , and the condition in which the part held on the head is not yet released can also be detected accurately. Furthermore, by changing the threshold value relating to the sensor amplifier output, it is possible to accurately detect the condition of the part at different positions such as the part-suction position and the part-delivery position. Since the part-released condition can be accurately detected in this manner, the need for a pusher for forcefully releasing the part can be eliminated, which also serves to reduce cost. 
         [0036]    The art may be embodied in other specific forms. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the art being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.