Part-delivery apparatus and method for the same

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.

BACKGROUND

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.

2. Description of the Related Art

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.

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.

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.

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.

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.

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

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present art will be described below with reference to the accompanying drawings.FIG. 1is a perspective view showing the general construction of a part-delivery apparatus according to one embodiment of the present art,FIG. 2is a perspective view showing the construction of a head assembly and its adjacent portions, andFIG. 3is 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 feeders12(respectively indicated by12A and12B) are held by suction onto six heads20(respectively indicated by20A,20B, . . . ,20F) and the six screws held on the respective heads are transported to a part pallet60and delivered to designated part-delivery positions on the part pallet60.

Heads20are arranged in two rows in the X-axis direction and three rows in the Y-axis direction shown inFIG. 1. The mechanism including head assembly20is movable in the Y-axis direction. Head assembly20is constructed so that the six heads together can be moved up and down along the Z-axis direction. Further, as shown inFIG. 2, the mechanism including head assembly20is provided with six upper-side positioning units42(respectively indicated by42A,42B, . . . ,42F) and six lower-side positioning units52(respectively indicated by52A,52B, . . . ,52F) in corresponding relationship to the six heads20.

FIG. 4is a plan view showing part-delivery paths from the feeders12A and12B to part pallet60(as viewed from the direction opposing the Z axis inFIG. 1). Parts (screws)10fed out of feeder12A in an orderly aligned manner are each loaded at a part-receiving position P1A directly into a cartridge14A serving as a loading device. As each part10is loaded, cartridge14A rotates 180 degrees thereby automatically transporting part10to a part-suction position P2A where corresponding head20can receive part10by suction. In like manner, parts10fed out of feeder12B are each loaded at a part-receiving position P1B into a cartridge14B and transported to a part-suction position P2B.

In this way, since each part10fed out of feeder12is loaded into cartridge14(14A or14B) and automatically transported to the position where corresponding head20can receive part10by 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 cartridge14is automatically transporting one part10to the part-suction position, feeder12can feed out next part10in an orderly aligned manner, which serves to shorten the takt time.

Then, head20A receives part10by suction at part-suction position P2A and transports it along the Y-axis direction for delivery to a part-delivery position P3A on pallet60. In like manner, heads20B,20C,20D,20E, and20F deliver parts10to corresponding part-delivery positions P3B, P3C, P3D, P3E, and P3F.

Six heads20transport parts10by arranging them with spacing “a” along the X-axis direction and spacing “b” along the Y-axis direction as shown inFIG. 4. However, on pallet60, part-delivery position P3C is displaced in the X-axis direction and part-delivery position P3F 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, heads20are not fixed, and a mechanism is provided that automatically accommodates the displacements between the part-suction positions and the part-delivery positions by positioning heads20by moving them up and down so as to pass through respective positioning units42and52.

FIG. 5is a diagram for explaining the positioning of heads20at the part-suction positions, andFIG. 6is a diagram for explaining the positioning of heads20at the part-delivery positions, both viewed from the direction opposing the Y axis. Each head20is provided at its center with a compliance mechanism22for allowing the movement of head20in a horizontal plane. Compliance mechanism22has a plurality of steel balls between two plates, and with these steel balls222rolling, head20is allowed to move in the X- and Y-axis directions within a predefined range.

As shown inFIG. 5, when taking part10from cartridge14, head20moves up passing through upper-side positioning unit42in contacting fashion and is thus positioned with respect to the part-suction position. After that, the ejector (not shown) connected to a part-suction coupling26is activated to draw part10onto head20.

Head20with part10thus held thereon moves to a position above pallet60. Then, as shown inFIG. 6, head20moves down passing through lower-side positioning unit52in contacting fashion and is thus positioned with respect to part-delivery position. After that, the ejector (not shown) connected to part-suction coupling26is deactivated to deliver part10onto pallet60.

In this way, when head20moves up and down passing through the respective positioning units, head20is fixed in a prescribed position by contacting the positioning units and thus positioned in place. Head20need only be made to contact each positioning unit so that head20can be fixed in a prescribed position for example, the positioning unit may be made to abut head20from four side or at a plurality of positions. Head20and its positioning units42and52are constructed so that upper-side positioning unit42and lower-side positioning unit52do not simultaneously act on head20.

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.

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.

FIGS. 7A and 7Bare diagrams explaining how the condition of the part is detected at the part-suction and part-delivery positions, respectively. As shown inFIGS. 7A and 7B, an optical fiber sensor24is mounted inside the tip of head20on which part10is held by suction, and the condition of part10is detected by detecting reflected light and determining whether or not part10is held on the head tip.

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 part10is not held on head20when part10is actually held on head20as shown inFIG. 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 part10is still held on head20when part10has been delivered to pallet60as shown inFIG. 7B.

For the part-delivery position, two threshold values may be set in order to discriminate three conditions, i.e., the condition in which part10remains held on head20, the condition in which part10is placed on pallet60, and the condition in which part10is neither on the tip of head20nor on pallet60.

By detecting the condition of part10using optical fiber sensor24as described above, an erroneous detection can be prevented from occurring due to pressure variations within head20, 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.