WHERE THE ACTION IS ….

It is common, when working with conveyor controls, automation or robotic systems, to synchronize the operation to the conveyor.  This practice is commonly called “line-tracking” and is accomplished by coupling an encoding device to the conveyor.  The encoder generates a frequency or position reference which is processed by the automation or robotic controller.

An encoder should ideally be coupled to the conveyor in such a manner that it is representative of the actual conveyor motion in the proximity of the controlled operation; in other words, close to the operation and free from the effects of back-lash, conveyor slack or erratic motion caused by conveyor wear.  Encoders are sometimes connected directly to remote conveyor drives or idler turns; unfortunately, this method, in many cases, does not provide accurate tracking of the conveyor motion at the point of the operation.  This can create inefficiencies in the operation as well as significantly increase the chance of collisions between the automation and the objects being conveyed.

A “parasitic encoder drive”, commonly referred to as a “line-tracker”, “caterpillar” or “synchronous encoder drive” … “goes where the action is”.  It provides accurate conveyor tracking.  These drives engage directly with the conveyor and can be installed in close proximity to the operation.  They can be set-up to measure “link” or “linear” travel of the conveyor, and with the encoder, ratioed to provide the desired resolution.

Edon manufactures a complete line of standard and heavy-duty line-trackers/encoder drives to fit most conveyors (i.e., 2", 3", 4", 6", enclosed types, flat-top, belt, roller and power & free, etc.).  And, we also engineer and build custom encoder drives for specialized conveyors.   Additionally, we custom manufacture guarding and drive train components for remote driven encoders.

Incremental Line-Trackers

The EDON incremental line-tracker engages with a conveyor, through the use of a mesh-dog system, to emulate or measure the conveyor velocity or position on a link-by-link basis.  Measurement is accomplished with an appropriately coupled incremental or absolute encoding device, or similar transducer.

The basic line-tracking mechanism consists of a heavy-duty aluminum or steel back-plate and frame.  Attached to the plate is a roller-chain and sprocket assembly driving a live axle. The   roller-chain is equipped with hardened mesh-dogs, so arranged as to permit engagement to the conveyor, to transmit motion to the tracking unit.  The live axle is geared to the proper ratio to drive the encoder/transducer to generate a signal analogous to conveyor travel. The dog pitch can be specified to accommodate various conveyor pitches. The output signal is fed to the automation controller to serve as a reference for automation or conveyor control.   Additionally, on heavy-duty units the back-plate is pressure compensated to maintain conveyor contact with the dogs, and to also facilitate jam-relief should a foreign object  become imbedded in the conveyor chain and wedge in the parasitic drive.  Limit switch outputs can be provided to indicate jam conditions.

Linear Line-Trackers

Similar in basic design to the incremental line-tracker, the linear line-tracker (an exclusive EDON development) is arranged with tandem drives one conveyor pitch out-of-phase with each other.  This enables linear measurement versus link measurement of conveyor travel.

By nature, the incremental line-tracker can be subject to error caused by wear between the conveyor links.  This can cause period-shifts in the encoder output which results in tracking errors.  One can somewhat compensate for this error via an “update circuit” in the PLC/PC if control distances along the conveyor are not excessive and if the incremental line-tracker is installed in close proximity to the controlled application.  On the other hand, if high-tracking resolution or accuracy is necessary the linear line-tracker is preferred since it compensates for conveyor wear and stretch in real time.  It produces a signal that is analogous to conveyor travel with consistent performance.

The out-of-phase tandem drives of the linear tracker are coupled with sprag clutches or electronically coupled via EDON smart-cat controller board. The combination of the out-of-phase arrangement with the clutches produces a mechanical addition to the encoder drive shaft rotation which compensates for the difference between link and linear conveyor travel.  This same affect is accomplished with the smart-cat controller except the mechanical shafting, gearing and clutches are replaced via software logic.  The Edon linear tracker is capable of measuring actual travel or object position in feet/inches/mm and the signal feed-back is not affected by conveyor link wear.  This feature is particularly beneficial when tracking objects which require direct contact with the automation.  Or, similarly, in conveyorized spray finishing when spray lead/lag, machine position, or the relationship of the control sequence start points in robotics is critical, and thus, close part registration is required. 

In paint finishing, significant paint material savings can be attained with an EDON linear line-tracker.  It is not unusual, on many  systems, for gun trigger on/off or lead/lag points to be set long or increased  to compensate for poor line tracking due to signal drift.  Signal drift is caused (generally) by conveyor wear, poor selection of line-tracker installation location, and/or old and new conveyor chain mixed within the system.  This compensation practice wastes paint material and causes heavy film deposition on edges and flanges and consequently rework and/or rejects.  An EDON linear line-tracker solves this problem!

ENCODER MOUNTING

Direct driven or geared encoders are generally mounted on the parasitic drive or optionally remote mounted with their gearing in an enclosure and shaft connected to the drive.  In either case, Nema-12 or explosion-proof enclosures can be provided by EDON to house the gearing mechanism and encoding device.  Plug connectors can also be optionally factory installed and wired ready for field plug-in. For remote-mounted encoders, EDON manufactures drive shafts with heavy-duty guarding, made to order, to accommodate field conditions.