The present invention relates to a synchronization control system that controls plural controlling object apparatuses such as screw tightening apparatuses or actuators while synchronizing them.
In a case in which plural screws are collectively tightened by using plural screw tightening apparatuses in a screw tightening process in a production line for products, a method is proposed in which output torques of the plural screw tightening apparatuses are increased step by step while synchronizing them in order to prevent inclination or rotation of a workpiece into which the screws are tightened (refer to, for example, Japanese Patent No. 3569619).
Further, in some cases in which positional control in plural axis directions is performed by using plural actuators (motors or the like), operations of the actuators are switched step by step so as to synchronize them at a point in time when the driving in all the axis directions is completed, and thereafter to perform the following driving.
However, operation characteristics of the controlling object apparatuses such as screw tightening apparatuses or actuators include variations due to their individual differences. Therefore, even if torque increase commands for increasing the output torque from a current same tightening torque to a same target torque are issued to the plural screw tightening apparatuses, all the screw tightening apparatuses do not necessarily reach the target torque, which results in time differences thereamong.
Further, even if positional commands to simultaneously reach respective target positions are issued to the plural actuators, in practice, the arrival times to the target positions of the actuators are mutually different in many cases.
In such cases, a signal indicating a synchronization waiting state may be output from each controlling object apparatus when reaching the target torque or the target position, and a synchronization determination may be performed when those signals are output from all the controlling object apparatuses to enter the following operation step (refer to Japanese Patent No. 3569619 and Japanese Patent Laid-Open No. 2001-100808).
However, in the synchronization control method disclosed in Japanese Patent No. 3569619, plural interface lines corresponding to the number of the screw tightening apparatuses are provided. Conversely, only the screw tightening apparatuses less than the number of the interface lines to be installed can be handled, which limits the number of the screw tightening apparatuses which can be synchronously controlled. On the other hand, if plural interface lines corresponding to a maximum number of the screw tightening apparatuses which may be used are provided in advance, it is necessary to prepare infrequently-used interface lines, circuits associated therewith, and the like. This is not economical.
Further, in the synchronization control method disclosed in Japanese Patent Laid-Open No. 2001-100808, a complex configuration using many wired OR lines with respect to plural signals TL1 to TLN and TLA is employed. Additionally, during one synchronization waiting state, for example, TL1 complexly changes from an on-state to an off-state to the on-state, and TLA as well complexly changes from an on-state to an off-state to the on-state. In such a case, it may take time for processing for synchronization waiting, or TLA returns to the off-state before detecting that TL1 changes to the off-state in each axis direction since a ON pulse width of TLA is too narrow, which may leave an apparatus behind in the detection processing.