A flux vector drive system provides on-the-fly bindery conveyor synchronization to reduce scrap and maintenance while boosting productivity
Everyone remembers that, as time went on, the old gray mare just wasn’t what she used to be. The same thing can happen to aging industrial equipment as it tries to cope with increasing productivity demands.
For example, coordination of two separate sections of a book bindery line, was turning into a maintenance and production nightmare for E. P. Graphics, Berne, Ind. As a printer and bindery specializing in book production, the company’s strategy for staying competitive includes refurbishing and updating older equipment to keep pace with ever more stringent production demands. Inevitably, when the older equipment would break down, replacement parts were hard to get, or simply not available. And, even when operating as originally designed, the scrap rate resulting from transient operations, as the bindery sections were brought up to speed and synchronized, was unacceptably high.
The binding process
E. P. Graphics uses a 1970’s vintage Dexter Perfect Binder for collating sections of pages, trimming and applying adhesive to the spine, adding covers, and trimming to final size. Basically, the bindery operation consists of three conveyor systems whose speed and position must be independently controlled and coordinated for efficient production.
Folded multipage sections (booklets) are collated and stacked on a conveyor in the gatherer section of the bindery machine. The booklets, at this point, do not have covers. The gatherer conveyor then twists 90 deg to bring the booklets into a vertical position for loading into the next unit — the infeed conveyor. From the infeed conveyor, the booklets are loaded into the final, carousel section.
The carousel section contains a series of vertical, spring-loaded pockets that are mechanically held open to accept a booklet from the infeed conveyor. Once loaded, the pocket clamps shut to hold the booklet for further processing. Then, the carousel carries each booklet to a rotary knife unit that trims the edge that is to be glued. Hot glue is applied to the trimmed edge, covers are added (held in place by the glue) and a conveyor moves each booklet to stations for trimming to final size of the top, bottom, and open-end edges.
Need for synchronization
During normal operation, the gatherer section must be periodically stopped. This can happen due to a paper jam at one of the caliper stations that collate and load pages onto the gatherer conveyor, or it might be the result of a missed page at one of the loading stations.
Regardless of what is going on at the gatherer section, the carousel section must keep moving, if even at idle speed, to prevent the glue (which dries in a matter of a few seconds) from drying before already-glued booklets are through the cover-adding stage.
After a gatherer section stop, it must be accelerated and coordinated with the speed of the carousel conveyor so booklets will be loaded in proper position on the infeed conveyor and within a carousel pocket. Joe Mauricio, CEO of E. P. Graphics notes, “We always had a scrap problem during a gatherer startup, particularly as the machine got older. Invariably, we would lose two or three books or cause a carousel jam while trying to synchronize the gatherer and carousel sections with our old restart and synchronization system.”
By guess and by gosh
After a shutdown, an operator used a mechanical clutch to restart the gatherer and coordinate its movement with that of the carousel. The original synchronization system consisted of an outmoded U. S. Bureau of Naval Ordinance resolver unit and a hand-built collection of components that timed the opening and closing of two micro-switches to achieve synchronization.
This system frequently broke down, due to its age, and replacement components were often not available. In addition, because of the age of the system, it was impossible to hold a set speed and the two sections would drift in and out of synchronization.
“Finally, we lost patience with this system and decided to upgrade,” recalls Allen Bertsch, E. P. Graphics maintenance supervisor. “Working with Complete Drives Inc., a Ft. Wayne, Ind., mechanical and electrical drive distributor, a new system was installed in 1991 that could accurately synchronize the two sections, run at higher speeds, and provide more reliability.”
Drive system configuration
The gatherer drive would have to respond quickly with both forward and reverse torque. It would also have to accelerate quickly; but, as synchronization speed was approached, decrease the rate of acceleration quickly to hold synchronization speed.
The gatherer drive chosen was a 15 hp, Thor Technology Series 7000 flux vector drive with dynamic braking, controlling a 15-hp vector duty ac motor (Lincoln Electric’s C-TAC), also from Thor.
The carousel drive was not as critical, because it was the lead drive, so a 10-hp AC Technologies DL Series variable-frequency drive and motor were chosen.
The two drives are electronically synchronized by a Drive Control Systems, Eden Prairie, Minn., SDC-2 synchronous drive controller and two Model 470, 1200 pulse-per-revolution quadrature encoders with index pulse (one on the gatherer and the other on the carousel) .
The SDC-2 requires an analog signal input proportional to carousel speed. A Drive Control Systems Chase 1000 follower control (digital to analog converter) converts encoder signals to a 0-10 vdc output.
When both sections are stopped, the encoders are set so both the gatherer and carousel are synchronized. When started, the carousel encoder sends its index pulse to the SDC-2. Immediately, the gatherer starts and sends its encoder index pulse to the SDC-2. Initial encoder set up is important because, when operating, the SDC-2 tries to match index signals for synchronization.
A proximity switch on the carousel sends a Start command to the SDC-2 and drive control when the gatherer is started. This proximity switch is set to pick up just prior to when the carousel encoder sends its index pulse.
With a five-decade thumbwheel the operator can either advance or retard the synchronization point in the SDC-2. This may be necessary if, for example, the gatherer conveyor is overloaded and, because idler tension is spring loaded, its conveyor chain jumps a tooth. The operator then adjusts the systems, using the thumbwheel switches, by either advancing or retarding the point of synchronization.
Another proximity switch on the gatherer provides a Stop command to the gatherer drive in the event of a jam. This provides an accurate stop position for restart. It does this by advancing until the gatherer encoder is near its index point (or rotates not more than 180 deg from that point).
A new lease on life
In the several years that the new flux vector drive system has been operating, it has indeed breathed new life into the old bindery at E. P. Graphics. The generation of scrap booklets due to poor synchronization with the carousel section after a gatherer stoppage has been virtually eliminated. Mr. Mauricio attributes a 10% to 15% reduction in the overall scrap rate of the entire binding operation to the redesign with the flux vector drive system.