The skilled art of airing a stack of sheets
To twist a stack of sheets to get air properly between all sheets and then lift it to a new position is a hard, heavy and highly skillful job. Each sheet quality and type of job has to be handled in its own way, which requires a nearly artistic operator skill as well as muscles. Automating this process has been a strong, but impossible wish among both factory owners and operators for a long time. Now Yaskawa introduces the first robot-cell in the world able to automate this process: Yaskawa Levanto
Yaskawa’s Skilled Human Touch airing process
Yaskawa Levanto is based on Yaskawa’s SDA robot, which is the world’s first and only humanoid, industrial dual-arm robot. Having two arms enable Yaskawa’s SDA robot to copy even the most complicated human working processes down to the tiniest detail, if it is equipped with the appropriate tools and guidance programs.
After a careful study of skilled operators’ working procedures, Yaskawa developed its Skilled Human Touch separation & airing program, which allows the SDA robot to handle all cutting jobs exactly as the operators do, because the dynamic interaction between robot and operator makes the robot profit from each operator’s accumulated skills and experiences.
Yaskawa’s Powerful Human Hand grippers
The human hand is a unique masterpiece, capable of gripping nearly any object without harming it, due to an immediate, appropriate and dynamic adjustment of the hand’s gripper pressure while it, at the same time, takes the object’s surface friction and flexibility into consideration.
Yaskawa’s Powerful Human Hand sheet gripper has a small upper gripper-pad with a slightly flexible, rotating, non-sticky surface, copying the function of the human thumb. The lower, broader and thicker gripper-pad has a firm non-sticky surface with soft round edges copying the palm of a hand. In combination with the dynamic pressure control it comfortably handles a wide range of substrate qualities and stack thicknesses. The lower gripper-pad sides have also holes so anti-static air is blown in between the sheets to make the airing process even more efficient. A sharp edge at the end of the lower gripper-pad allows it to separate the selected stack from the pile within µ-mm accuracy.
Yaskawa’s Pile Topography Scanning system
The nice, flat topography of an unprinted pile of sheets can easily turn into the most unpredictable topography after printing and drying. For the skilled operator this might be a nuisance, but not a problem, while it is an impossible obstacle for any normal automation system. But without solving the topography challenge, separating a stack from a pile cannot be automated.
Yaskawa’s Pile Topography Scanning system scans the pile topography and adjusts the gripper movements accordingly each time it starts to build up a new stack on the vibration table. Sheets with more inks on one side than the other, “waves” caused by the drying process, as well as up- or down-turning corners are easily handled by Yaskawa Levanto and its dynamic Pile Topography Scanning system.
Pile turning of sophisticated covers
Sophisticated covers with high ink densities and coatings always leave the printing press/off-line-coater with the cover-side upwards. Most cover feeders in saddle-stitchers and collators require that the covers are fed with the cover side downwards, which requires a pile-turning between printing and finishing. Apart from a pile turning takes time, it also removes productive time from printing or cutting, if the printer or cutter operator runs the pile turner.
Yaskawa’s integrated Stack Turning Process
Installing Yaskawa’s SDA 20 robot behind the vibration table implies a vertical stack feeding directly into the register corner of the vibration table while the stack at the same time is turned front to back without any loss of time. If the job does not require a pile-turning, the vibration table can be installed on an optional turntable, which turns the vibration table 180º and allows the robot to feed the vibration table from the front.
If a turntable is not installed or if a special job requires manual feeding of the vibration table, the change between robotic and manual operation is fast and unproblematic, because the robotic safety-zones in front of the vibration table are minimal. Finally, as the space behind the vibration table normally is unused, Yaskawa Levanto can, in practice, be installed without occupying any extra space.
Yaskawa SDA 20 dual-arm robot
With a lifting capacity of 40 kilos (depending on how far it has to reach out), Yaskawa SDA 20 is the most powerful SDA robot. Each arm has 7 axis, the two Yaskawa grippers adds two more, and with the center axis and the vertical socket a total of 18 axis gives SDA 20 an unmatched operating flexibility, close to a human being (a standard robot has 4-6 axis).
Yaskawa Levanto performance
Yaskawa Levanto has a maximum lifting capability of 30 kilos combined with a maximum handling width between the robot arms of 165 cm and a maximum stack thickness of 50 mm (a 50 mm stack of 64*90 cm sheets weights roughly 30 kilos). Depending on lots of various job criterias Yaskawa Levanto handles, in practice, 4-5 pallets per hour (75*106 cm/42”) with pile heights of up to 120 cm.
125 cm Lifting Socket
In the process of separating the stack from the pile the SDA 20 robot is elevated up to 125 cm by the spindle in the socket, so Yaskawa Levanto handles sheet sizes of up to 125*165 cm (extended 7B/65” printing press format). It can turn a full 360º on its socket, so Yaskawa Levanto can handle two vibration tables (and sheet cutter lines) if the average job has a lot of cuts (f.ex labels) or two lifting tables for non-stop production of short run jobs with very few cuts (f.ex magazine covers).
Yaskawa lifting table
The Yaskawa lifting table is controlled by the SDA 20 robot, so it always separates the stack from the pile at the same fixed height. This reduces the cycle time to a minimum and makes the stack collection and the sheet separation & airing process fast and reliable.
The lifting table has one lock-bar, which prevents sensitive sheets from being pushed out of position when the grippers separate the stack from the pile. A second lock-bar between the stack and the pile locks the position of the upper sheets in the pile, when the stack is drawn backwards from the pile by the robot during the separation process.
Yaskawa’s unique lifting table is accessible from two directions, so the SDA 20 robot can access the pile from its position behind the table, while the operator can change pallets from the front without entering the robot’s safety area.
Modified Vibration table
Yaskawa Levanto works with most conventional vibration tables from the leading manufacturers, but the table must be modified. The most convenient option is to change the existing table with a Yaskawa re-conditioned and modified vibration table configured for Yaskawa Levanto.
Yaskawa Levanto controls the vibration table air-supply, vibration timing & frequency as well as the air-flow through the added air-nozzles & air-escape-nozzles in the back-plate. The standard lock-bar is also controlled by the robot and is modified to secure a correct vertical stack delivery and a control of the sheet-movements, when the robot releases the stack on the table. The control cabinet is enlarged and integrated into the central control cabinet.
The standard lay-out positions the SDA 20 robot in the free space behind the vibration table to minimize the space requirements and to eliminate conflicts between operator and robot in relation to safety areas. In this configuration the stacks are always delivered from the back with an integrated stack turning. The vibration table can be installed on an optional, robot controlled, turntable, which turns the vibration table 180º to be emptied in the normal way. It then turns it 180º back ready to be fed again by the robot. In this configuration SDA 20 can feed the vibration table from both front and back – without and with stack-turning.
Optional automatic stack delivery system
The optional automatic stack delivery system empties the vibration table onto an air-cushion storage table. Here it waits until the operator requests it to be delivered automatically to the air-cushion table next to the sheet cutter. From this position the operator can collect the stack without moving from the working position so focus can be maintained totally on the central task: sheet cutting.
Stipulating that the operator uses around 20 sec to collect a stack on the vibration table and move it back to the sheet cutter and stop and start the robot, around 8 minutes/hour of effective cutting time is lost (+13% - 1 operator & 4 full 40” pallets/hour) without the automated delivery.
Optional conveyer system
The lifting table is prepared for an optional conveyor feeding & emptying system. A number of fresh pallets can be aligned and stored on the conveyer behind the lifting table, and as soon as the robot has removed the last sheets from one pallet it is automatically removed and replaced with a fresh pallet from the conveyor. The changing time is around 40 sec, but as it partly runs parallel to emptying the vibration table the effective time added to the production cycle is only around 25 sec per pallet change.
Stipulating that an operator uses around 90 sec for a manual pallet change (without pile-turning) the conveyor systems increases the net production time with more than 4 minutes/hour (+7% - 1 operator & 4 full 40” pallets/hour). If pile-turning also has to be considered another 4-6 effective sheet cutting minutes are lost without the conveyor system and integrated stack turning feature.
Pallet changes and pile turnings do not depend on the number of sheets on the pallet, so the impact of fast and even non-stop pallet changes and integrated pile turnings increases dramatically in short-run productions with, say, 1,000 sheets instead of 7,500 sheets on a pallet!