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Robot packages powder products
January 29, 2014
7 Min Read
With more than 2.2 million members representing more than 60 percent of all Swiss households, COOP is a Swiss cooperative society whose core business is retailing. COOP has various sales formats in the food, nonfood and service sectors and is the second largest supermarket chain retailer in Switzerland, with a 32-percent market share of the country's supermarkets.
In 2005, COOP's production and packaging center in Pratteln was looking for a case packer for pouches of dry products, such as sugar, coffee and baking mixes. "Products in granular and powder form behave as fluids in bags," says COOP project coordinator Dominik Leder, who is responsible for the planning and implementation of technical projects, as he explains the core problem in optimizing the end-of-line packaging for these products. "We were aiming for a flexible system that can package these products quickly and reliably," he says. Another requirement is a system that can cope with Duopacks (two standard packs fastened together) weighing up to 1,000 g.
The COOP team was anticipating a traditional case packer, but then, a newly developed, robot-based system entered the picture: the RobTeq Speed-Picker from Skinetta Pac-Systems Corp. (www.skinetta.com), which incorporates a pick-and-place robot from ABB Robotics Div., (www.abb.com/robotics). "We were very skeptical about whether there was a robot system that would even be able to hold our products, due to the centrifugal forces," remembers Leder. "But this unit solved a whole range of problems for us. Above all, the changeover times and maintenance expenses could be drastically reduced." This is because the abrasive, sticky contents of damaged bags cause a high level of wear in conventional case packers, whereas there are considerably fewer mechanical parts in the RobTeq Speed-Picker.
Initially, the way to achieve this was anything but clear. "We were aware that we would have to break away from the norm if we wanted to design a low-maintenance, fast and extremely flexible end-of-line packaging machine. The ABB Flex-Picker seemed to be the new way forward," says Norbert Wörz, head of production development at Skinetta.
The ABB team involved did not wish to rule out the possibility that the design of such a machine could succeed with the Flex-Picker. However, this was not a certainty. Nevertheless, this spurred on the engineers at Skinetta, which has become a specialist in innovative solutions since the change of management about a year ago. The Skinetta team had a number of problems to solve, the main one being the inertia of packing the bags. "It is as if you were to attach a heavy stone to a long rope and then pull quickly on the rope. Your arm accelerates very quickly and without much effort, until the rope is taut. When you then encounter the gravitational pull of the stone, it initially feels as if the stone is hitting your arm," says Wörz, describing the phenomenon.
To eliminate this problem, Skinetta first had to optimize the suction system on the robot that picks up the bags. The suction performance of conventional systems was insufficient to transport 1,000-g bags reliably and at the necessary speed. To absorb the weight resistance of the content, a special movement curve was calculated for the gripper. Says Wörz, "Only with this combination did we find it possible to place the bags in the cartons at high speed."
COOP liked this concept. "Nowadays, we need to be much more flexible than a few years ago," says Leder. The Pratteln facility stocks five distribution centers, each of which supplies about 1,000 local businesses and shops. Sales are reported to the distribution centers and simultaneously to the Pratteln packaging center via an enterprise resource planning system, and packaging is carried out as required. The number of package sizes is also increasing. "The trend is for package sizes that exactly fill the shelf," explains Leder. Above all, products that have a low demand should be delivered at a precise time and in small quantities.
The packaging center also delivers directly to the shops, bypassing the distribution warehouses. This allows COOP to react quickly to unexpected purchasing trends. The construction of the RobTeq Speed-Picker is designed to accommodate this quick and flexible packaging. Only the suction cup has to be replaced to handle a different package format, and a new locking mechanism makes changeovers easier. Even the mechanical pregrouping of the bags is a thing of the past. The Speed-Picker, which packages up to 88 bags/min, picks up randomly located bags directly from the conveyor, because the ABB Flex-Picker is synchronized with the conveyor belt.
The Skinetta line runs 20 different pouches ranging in size from 100 to 500 g. The pouches are delivered to the operation with the bottom end leading. As they enter the machine, a rotating brush pushes them to one side of the conveyor, so they are in a straight row, after which a laser sensor detects the leading edge of each pouch. The robot's controller also knows the conveyor speed. This establishes the location of each pouch for the Flex-Picker without requiring a collation system or an expensive vision system. The system can track of up to 256 bags on a conveyor, although the COOP unit has a smaller conveyor.
The robot picks up each pouch with suction cups, while the conveyor continues to move, and places it in the waiting carton, which has been erected in another section of the machine, and delivers it to the robot with the top open and the top flaps held back. Cases contain from six to 10 bags in up to three layers. All of this information is part of the programming of the robot. Because product settles toward the bottoms of the bags, they are thicker at the bottom than at the top. Therefore, to achieve a balanced pack in the cases, the robot turns alternate bags 180 deg so the thinner top sections overlap each other in the center.
A laser sensor inspects the top of the case after it is filled to check for missing or misplaced bags, after which the top flaps are sealed with hot-melt glue. The cases then travel over a checkweigher on their way to palletizing.
The RobTeq Speed-Picker incorporates a Model S7 PLC and a human/machine interface from Siemens Energy & Automation, Inc. (www.automation.usa.siemens.com). The PLC stores operating parameters for all of the bags and products in memory, and the operator can select parameters for the products running from the HMI. Packaging plans can also be programmed off-line using MS Excel, and the data can be imported. Says Leder, "Once Norbert Wörz reprogrammed the machine as part of the acceptance procedure, all of our doubts were dispelled."
As mentioned previously, the suction-cup design was critical for proper bag handling, and a number of different designs are required for the range of bags that the unit runs. The good news is that these require only about 30 sec to change so they do not impact the changeover from one bag to another.
The RobTeq Speed-Picker allows COOP to react to increasing economic demands. Says Leder, "We have the increasing pressure of cost on the one hand and growing customer demands for more flexibility, speed and quality on the other hand." For example, products run at COOP can also be produced or packaged by other manufacturers. In fact, the center in Pratteln recently lost the task of roasting and packaging peanuts to an independent competitor. "After a year however, some products have come back simply because our product quality is right," says Leder. Conversely, COOP also packages for other manufacturers, and the facility would like to expand this.
COOP installed the first RobTeq Speed-Picker in July 2005 and has plans for additional units this year and next.
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