Conventionally, trucks in a conveyor are driven by a driving chain. In such a conveyor, the driving chain is moving at all times even while the trucks are stored in storage lines, which promotes occurrence of wear of the driving chain as well as noises. Moreover, in order to start the trucks, it is necessary to engage the driving chain with the pressure plate provided to the trucks, which causes a shock at the time of engagement. Such a shock of course becomes greater in proportion to the speed of the driving chain. For these reasons, the upper limit of the speed of the conventional conveyor has been some 18 meters per second. Thus, the conventional chain drive conveyors are not suitable for high speed conveyance.
One solution of this problem is to use a conveyor driven by linear motor. In known linear motor drive systems, primary members of linear induction motor are provided on the floor and reaction plates which constitute the secondary members of a linear induction motor are provided to the trucks, respectively; and by maintaining the gap between the two members accurately and energizing the primary members, the trucks are electromagnetically propelled.
However, if there is a horizontal curve in the conveying path, the locus of the reaction plate is likely to be diverted from the primary members; and if there are curves or undulations in the vertical direction, the reaction plates are subjected to movements up and down. Thus, there occurs unevenness of the gap, which will result in instability or reduction in the propelling force. Consequently, conventional linear motor drive systems have been used only in straight conveying lines.
Accordingly, one object of this invention is to provide a linear motor driven trolley conveyor which is capable of stably driving trucks even where there are horizontal curves or slopes in the conveying path.