Abstract: In an assembly line in which at least two kinds of workpieces are transported by mixture and in which each of the workpieces is transported by a self-propelling transporting member, a transporting pitch for each kind of workpiece is set in advance based on a difference in the number of assembling man-hours required for each of them. The timing for starting the transporting member off a starting end of the assembly line is controlled according to the transporting pitch such that a pitch between a preceding transporting member and a succeeding transporting member becomes equal to that which is set for a workpiece to be transported by the preceding transporting member.

Abstract: A conveying carrier is arranged to be self-propelled and move along a conveying passage having a pit formed therebelow. A track covers the top side of the pit flush with the road surface of the conveying passage. A plurality of wheels are attached to the conveying carrier with at least the front wheels being casters. A steering frame is pivotally supported on the conveying carrier and is turnable about a vertical steering axis line. A driving wheel and motor are attached to the steering frame, with the driving wheel being positioned to contact the track at a location substantially directly below the vertical steering axis line. A guide member is guided by a guide rail laid in the pit and connected to the steering frame through a slit in the widthwise center of the track. The pit is a substantially U-shaped track frame buried in the widthwise central portion.