Recently, along with the advancement of electronics revolution, further enhancement of productivity is also required in electronic parts mounting machines. Conventional electronic parts mounting machines are described below while referring to FIG. 2, FIG. 3, and FIG. 4.
FIG. 2 shows a schematic constitution of an electronic parts mounting machine. Reference numeral 1 denotes a rotary head, which mounts parts by means of plural nozzles 2. Reference numeral 3 denotes an X-Y table, which fixes a board to mount parts on, and positions the board beneath the nozzles 2. Reference numerals 4L, 4R are parts feed units, and plural parts cassettes (parts feed means) 5 are mounted on each one thereof, and desired parts cassettes are positioned beneath the nozzles 2. Reference numeral 7 denotes a controller, which controls the entire electronic parts mounting machine. Reference numeral 10 is an indicator warning the shortage of parts to the operator, 11 is board carrying means, and 12 is board discharge means.
Referring now to FIGS. 3(a)(1), 3(a)(2) and 3(b)(1) to 3(b)(3), the operation of parts feed units 4L, 4R (hereinafter shown merely as L and R) is described. FIGS. 3(a)(1) and 3(a)(2) show the configuration of parts cassettes 5 in the parts feed units L, R. Both parts feed units L, R are in completely identical parts layout. This is intended to continue production by other parts feed unit R or L if parts are used up during production in one parts feed unit L or R. FIGS. 3(b)(1) and 3(b)(3) show the motion of the parts feed units L, R in the event of parts shortage during production. In the state shown in FIG. 3(b)(1), the parts feed unit L is in the process of production in the active position, while the parts feed unit R is located at the parts refill position not interfering the parts feed unit L. Herein, when parts shortage occurs, it is changed to the state shown in FIG. 2(b)(2). That is, the parts feed unit L moves to the parts refill position, and the parts feed unit R moves to the active position to continue production. The operator refills the parts feed unit L. When further parts shortage occurs, the state becomes as shown in shown in FIG. 3(b)(3). That is, the parts feed unit R moves to the parts refill position, and the parts feed unit L moves to the active position to continue production. By thus exchanging the parts feed units L and R, drop of operation rate due to parts shortage is prevented.
The conventional parts mounting method employing such plural parts feed units is specifically described below by referring to the flowchart in FIG. 4. Parts are sucked to the nozzles 2 from the parts feed unit L (step #101), and it is judged if there are parts or not (step #102), and if there are parts, parts are mounted on a board fixed on the X-Y table 3 (step #103). It is then checked if all parts to be mounted on the board by this mounting machine are completely mounted (hereinafter called EOP) or not (step #104), and the operation of steps #101 to #103 is repeated until reaching the EOP. When reaching the EOP, the mounted board is discharged, and next board is sent in (step #105).
On the other hand, if shortage of parts is detected at step #102, the parts feed unit L is moved to the refill position (step #106), and production is continued by the parts feed unit R (steps #107 to #111). Herein, steps #107 to #111 are same in processing as steps #101 to #105. In the midst of steps #107 to #111, if parts shortage occurs at step #108, the parts feed unit R is moved to the refill position (step #112), and it is judged if the parts feed unit L running short of parts in the first place is still in the process of parts refill or not (step #113), and if it is in the process of parts refill, production is stopped due to parts shortage (step #121), or if parts refill has been complete, going back to step #101, production is continued in the parts feed unit L.
In such mounting method, however, unless parts are refilled immediately by the operator, both the parts feed units L and R may be out of parts, and production may be stopped, so that the operation rate may decline. In particular, in the nighttime when the number of workers is small, it was difficult to operate continuously for a long time.