Conveyors are used in a number of applications to convey articles from a first point to a second point. Some common conveyor types include roller conveyors, which are typically comprised of a plurality of motorized and non-motorized rollers, and belt conveyors, which include belts that are driven by one or more motorized rollers. The conveyor may be controlled by a single centralized controller, or may be divided into multiple sections, or zones that are each controlled by a separate controller. In either case, the one or more controllers generally control the conveyor system by selectively activating motorized rollers or motors that operate the belt of the conveyor to move an article along the conveyor. In conventional conveyor controllers, the controller may also determine whether an article is being conveyed based on signals from presence sensors configured to detect the presence of an article on the conveyor, such as photo-eye sensors.
Motorized Drive Roller (MDR) conveyor systems use conveyor rollers that are driven by electric motors to move articles along the conveyor route. These types of conveyor systems typically include multiple independently controlled zones, with each zone having a single motor and an article presence sensor operatively coupled to a zone controller. The rollers of a zone are typically coupled to the driven roller so that the rollers operate in concert to selectively move an article through the zone in response to activation signals from the zone controller. The zone controller may be operatively coupled to adjacent zone controllers so that activation of the zone can be coordinated with the movement of articles upstream and downstream of the zone. A conveyor system may be implemented by arranging a plurality of these zones sequentially so that articles are transported in the conveying direction. These zones may include straight sections, curved sections, diverting sections, and merging sections so that articles may be received from and discharge to multiple locations. The modular characteristics of MDR conveyor zones facilitate reconfiguring conveyor systems by adding, removing, and reconfiguring zones within an existing conveyor system. An existing MDR conveyor system can thereby be changed and expanded as the needs of the conveyor operator evolve.
To achieve efficient conveyance of articles, a conveyor system should convey articles with short intervals, or gaps, between articles. Short spacing intervals increase article traffic density, and thus conveyor system throughput for a given conveyor operating speed. Short spacing intervals also reduce the overall length required in accumulation conveyor systems for a given article accumulation capacity. However, in order to prevent articles from colliding and/or being delivered to the wrong destination, conventional modular conveyor systems limit the number of articles to one per zone. Achieving short spacing intervals in a modular conveyor system using conventional zone controllers therefore requires short zones. This short zone requirement can significantly drive up costs of conveyor systems that have long spans or that accumulate large numbers of articles due to the large number of zones required to span the length of the conveyor system.
Consequently, there is a continuing need for improved methods and systems for modular conveyor control that reduce the cost of implementing modular conveyor systems, and that maintain or increase efficiency and throughput of modular conveyor systems.