Robots Reduce Bottleneck in High Speed Wraplines
December 1, 2005 By Pulp & Paper Canada
Most paper mills that get rolls ready for shipment have a common challenge: all paper that is manufactured on wide paper machines, and all paper that is wound up and slit into multiple rolls must pass…
Most paper mills that get rolls ready for shipment have a common challenge: all paper that is manufactured on wide paper machines, and all paper that is wound up and slit into multiple rolls must pass through a ‘single’ wrapline in the finishing department. In order to optimize/reduce this bottleneck that is a critical part of the operation where every product needs to pass through without having redundant equipment, the actual production demand needs to be met or overcome in terms of equipment (speed and automation) and people (operating and maintenance crews).
The average wrapline in North America produces approximately 70 rolls per hour, while about 15% of the mills run 80-150 rph. Less than a handful of peak production mills run up to 180 rph, which equals one roll every 20 seconds to be scanned, weighed, measured, wrapped, head-inserted and labeled. Just imagine the potential bottleneck at the latter rate for which robotic head and label applicators, very fast moving equipment and very quick PLC-to-host-computer handshakes are essential.
Putting aside the fact that very old equipment amplifies the bottleneck effect, because antiquated equipment is more labour intensive (mostly manual operation; 3-4 operators per shift) and more shut-down prone (due to increased main-tenance and fixes), in terms of new equipment and skilled operators the above throughputs can be translated into the following automation chart:
With semi-automatic wraplines up to 60 rph, one operator can place inner and outer heads manually, while the second operator would replenish consumables, such as wrapper stock/ heads/ labels, and take rolls to the warehouse. Over 60 rph, this task is more challenging and automatic label placement would be the next step.
With fully automated 60-180 rph wraplines, one operator can supervise the operation, respond to alarms and replenish wrapper/head/label stock, while it might take several clamp truck drivers to haul rolls away from the wrapline’s storage conveyor to the warehouse.
While brown paper rolls are typically not wrapped (often just strapped), and while tissue rolls are frequently stretch-wrapped (radial or axial or radial and axial wrapped), this article focuses mostly on ‘kraft wrapping’, because most white paper rolls are usually wrapped with one or two layers of conventional kraft paper for already-known reasons:
* It provides the best roll protection (especially the edge and bottom of roll)
* It allows the fastest wrapping cycle (least amount of revolutions per roll)
* Plastic is an adverse material in paper mills (finds its way to the pulpers)
* It is the printing industry’s preferred method for easily removing and recycling wrap.
Because ‘automated’ equipment is more reliable, more consistent, safer and less error-prone, it helps widening the bottleneck in any wrapline operation.
Per above chart, the following describes different degrees of automation that are used in various roll finishing operations:
1.Typical Automation (30-60 rph Wraplines)
* Automatic roll handling
* Automatic wrapper stock selection, dispensing/ glueing/ cutting/ tension control
* Automatic crimping
* Automatic turning rollers (in synch with dispenser & crimper)
2.Enhanced Automation (60-100 rph Wraplines)
* Above automation, plus:
* Automatic bar code scanning
* Automatic roll verification (weighing, width & diameter sensing)
* Automatic label application
* Optional, automatic inner and outer head placement
3.Full Automation (100-180 rph Wraplines)
* Above automation, plus:
* Automatic inner and outer head placement (via robots, vacuum conveyors, or combination of robot and vacuum conveyor)
* Very fast moving equipment:
* high speed roll conveying (90 fpm)
* high speed roll indexing (150 fpm)
* high speed wrapper dispensing (350 fpm)
* fast host computer response time (two seconds)
* Separation of wrapping and crimping station
* In-Line operation of wrapper/crimper/header
* Larger diameter wrapper stock on backstands (60″)
* Dual printers
* Glue system with bulk hopper feed
* Heads-picking from pallet stacks on auto turnstiles
General Aspects about Robots:
Robots used for the paper industry derive from the automotive industry, and standard car robot models that are used in mills are much more rugged than required for the weights to be lifted (can handle payloads up to 130 kg), are over-designed for the movements and speed demands, and thus wear is minimal. Storing spare robots is not customary and the first routine check-up/overhaul is not due until 5-10 years from initial start-up.
While mechanical robots are typically shipped from Japan, the controls, end tools and external cabling are designed and manufactured locally (in our case North America). Because downtimes are even less acceptable in the automotive industry, support is readily available in North America, such as a 24/7 helpline with a dedicated assistant.
The controls language is different from what mills are used to. It is not the typical PLC ladder logic and requires programming to be performed by the OEM. However, most robots are equipped with ‘learning pendants’ that can be used to teach the robot new movements.
Robots have six axis movements and thus a large work envelope with the ability to reach overhead and behind. They feature head location sensing abilities and can be programmed for various size heads. Because of the non-linear robotic arm movements, the entire area needs to be fenced off, and gates be equipped with redundant disconnects.
Picking a certain robot brand name/manufacturer, such as Fanuc, ABB or Motoman is not as important as a ‘good working relationship’ between the wrapline OEM and the robot manufacturer itself. Needless to say local support is always beneficial.
Robotic Head Placement:
If one robot can reach both sides of a wrapline’s crimper and/or header press, the robot is equipped with a ‘dual end tool’ to pick up two heads when going to the stack (see picture below). The movements to pick up two heads and reach both sides of the wrapline reduce the line speed to approximately 120 rph, but it eliminates the need for one of two robots. At higher speeds up to 180 rph, one robot is required for each side, which means a total of four robots (two robots for crimper, two robots for header press).
Robotic Label Placement:
With 180 rph wraplines, one robot can pick up a single label and apply it to the roll in 20 seconds or less. However, the printer needs to have the label printed by the time the roll arrives, which means that, while one printer is ejecting a label that is being picked up by the robot upon roll arrival, the other printer is already receiving the next roll’s data from the host computer.
Robotic arms ensure wrinkle-free and perfectly square placement of customer labels on roll ends and/or bilge.
Because robotic arms have a limited reach, they can be placed or retrofitted for head placement only if there is ample room for storing header stock very close to the crimper and header press. However, vacuum belt conveyors can be used for overcoming space restrictions and distances to transport heads to the robots/wrapline.
While it is fairly straightforward to lay out a new wrapline in a new or wide open building, re-working existing wraplines can be much more challenging and requires detail
ed engineering experience and innovative thinking for finding the best solution.
While automation can often be justified by reducing manual labour and by increasing reliability and consistency and thus decreasing bottleneck, justification for robots is also related to total roll production and becomes necessary over 80 rph.
Jan Gronewold has 20+ years of experience in the paper industry. He is a regional sales manager for Advanced Dynamics who has a 35% and growing market share in manual and automatic kraft-wrapping systems in North America, with 5 robotic installations that run between 90 and 180 rph. Advanced Dynamics also designs and manufactures Automatic Bale Dewiring and Pulper Feed Systems. For questions, please call the St. Bruno Quebec office at (450) 653-7220.
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