In our way of thinking, this includes even the smallest motorized components, such as DC-powered conveyor rollers. Motorized rollers provide a greater degree of material handling automation resulting in greater reliability and higher efficiency, as well as improved safety.
Traditionally, plants used mechanized conveyor systems such as chain and sprocket rollers, line shaft and large belt drives to move conveyor lengths. Today, plants are upgrading to smart conveyors using motorized roller technology that integrates a DC brush or brushless motor into the roller tube.
This solution is inherently safer, quieter, more efficient, easier to install, and requires no maintenance. It also offers the option of easily cycling the conveyor zone only when materials are present as opposed to a continuously running conveyor system, as is common with mechanical transport technology. This reduces maintenance and noise emissions, prolongs the life of the conveyor rollers and consumes less energy than traditional conveyor systems.
Motorized rollers require a certain level of control in order to program the operation of the conveyor and interface with other plant and conveyor systems. Several motorized conveyor manufacturers have integrated zero pressure accumulation (ZPA) controls into their conveyor systems to increase intelligence and control capabilities. Using a simple photoeye sensor to monitor package or material presence, the control cards activate and sequence the controlled conveyor zone only as needed. This way, the closed-loop control systems can automate a conveyor zone to prevent packages from colliding and causing bottlenecks.
Typical accumulating conveyor controls provide signal processing, 24 VDC motor input voltage, motor protection (fuse), and current limitation. Ideally, the system will allow for basic conveyor control functions such as accumulation, indexing, forward/reverse travel, dynamic braking, and speed control. In its simplest form, ZPA control moves packages along only when they are present in the conveyor zone and the signals may be linked to either a PLC or PC-based control system.
It is becoming ever-more crucial to expand these systems beyond closed-loop control. As fieldbus protocols continue to gain acceptance in the manufacturing industries, device-level components should be able to interconnect with other networked-based control systems.
With proper programming, conveyor components can adjust activities according to overall plant flow. If human error results in a product backlog upstream, the controller might signal a conveyor zone downstream to halt operations until the jam is cleared. This will prevent potentially dangerous and damaging collisions, while reducing downtime and speeding up re-starts.
Further, if a backlog is detected upstream, the system can reduce production downstream until the rest catches up. The information log can then be used to reassess production capabilities.
While DeviceNet is the most common protocol in materials handling, Ethernet-based controls are gaining rapid acceptance and capability, even down to the device level. Device-level suppliers must equip their components with the capability to accommodate system expansion. Currently, there are ZPA controls on the market that are ready for this change.
By installing DC motorized conveyors and controls in multiple, small, closed-loop systems, plant intelligence is increased, while the capability for system expansion stands at the ready.
While device manufacturers, machine builders, and end users hope a single fieldbus protocol will emerge, no standard has been established. This requires component manufacturers to build devices that accommodate all protocols. From sensors to actuators, the same need exists for motorized conveyor rollers. For now, it is logical for these suppliers to build devices compatible with the most prevalent protocols and design new versions as demand increases for others.
Engineers making material handling system decisions would be wise to evaluate automated solutions for the ability for advanced PLC or fieldbus-based plant controls. Retrofitting conveyor systems with fewer mechanical drives by using zero pressure accumulation controls and driven-roller technology will increase reliability, produce more streamlined, efficient operations and improve plant safety. Overall, conveyor automation is a step in the right direction to a fully automated plant.
Ken Bobick is Global Product Manager-RollerDrive for material handling system developer and manufacturer Interroll Corp. Learn more about the company at www.interroll.com.
