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Robotic palletization protects Sandvik

Automated lifting and stacking of heavy boxes onto pallets helps this maker of mining products avoid worker injuries and $120ꯠ of additional labor costs.
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FILED IN:  Controls  > Strategy
     

Faced with an insurance company's mandate to hire additional employees for safety reasons Sandvik Rock Tools instead invested in an automated robotic palletizing system. It lifts and stacks the company's heavy boxes of mine bolt resins onto pallets eliminating the risk of worker injury associated with manual stacking. In December Bristol VA-based Sandvik installed an RL-series linear robotic case palletizing system from Reis Robotics (Elgin IL). Equipped with an Allen-Bradley (Milwaukee WI) bar-code scanner the palletizer scans a pressure-sensitive bar-code label at one end of each case. That information is processed by the system's control network and instructs the robot to transfer the case to one of six pallet positions. Pallets are positioned in a row on the floor parallel to and beneath the linear track that the robot rides along. A slipsheet hopper is also located on the floor with three pallet positions to its left three to its right. This shortens the distance the robot has to traverse to place the sheet between layers on any of the six pallets. The Reis system palletizes 40- to 65-lb cases of mine bolt resins that are used to secure roofs in mining operations. Produced by Sandvik's Chemical Products Div. these mine bolt resins are made up of two components: a slurry-like mix of liquid polyester resin and limestone and a benzoyl peroxide paste catalyst. Both product components are filled into one capsule made of 2-mil clear polyester film supplied primarily by Hoechst Diafoil (Greer SC). When properly inserted in the roof of a coal mine the film breaks causing the resin and catalyst components to mix and rapidly harden into a grout that holds the roof in place reducing the chance of the mine caving in on workers below. Altogether the Reis system handles some 250 resin SKUs. Capsules measure either 22 or 32 mm in diameter. Between 32 and 48 cylindrical capsules are hand packed into cases supplied by Stone Container (Chicago IL). Cases typically are 250#-test C-flute corrugated. They vary in size from 19" to 66" L x 5" to 71/2" W x 31/2" to 51/2" D. Filling is executed on eight Model 40 Series chub packaging machines from BWI KartridgPak (Davenport IA). According to Sandvik manager Ken Monyak the machines are outfitted with two fill tubes that create a two-compartment package one for the resin and another for the catalyst. Once filled sealed and clipped operators hand load the capsule into the case. When the case is full plastic strapping is wrapped around it before an operator hand applies a pressure-sensitive label to one case end. A thermal-transfer printer from Sato America (San Francisco CA) prints a bar code product identification code production lot number use-by date product design description and box contents description onto each label. Scanning the case label Cases are conveyed out of the building across a parking lot where the conveyor is covered and into a finished goods facility. Cases continue on to the infeed conveyor of the Reis system. This approximately 30'-long steel roller conveyor is made by Roach Conveyors (Trumann AR). Conveyors were purchased throughRoach distributor Thomas Conveyor &Equipment (Hillside IL). About 10' from the end of the infeed conveyor a photoeye senses the presence of a case. An Allen-Bradley SLC 503 programmable logic controller signals a metal pop-up stop plate to lift. This plate prevents the case from moving downstream to the robotic pick-off station. When the pick-off station is empty the plate is instructed to descend to its home position allowing the case to continue to the end of the infeed conveyor where it comes to rest against a stationary metal end plate. An Allen-Bradley scanner mounted to the conveyor reads the bar-code label on the case. The code is sent to the PLC which compares it to an internal data table of label codes for all the SKUs. (Since the codes are only 13 characters long all SKUs can easily fit in the PLC's memory instead of having to link it to an external computer that would contain a separate database.) If the code doesn't match or if the label is missing or unreadable the PLC will instruct the robot to lift the case and place it onto a 15' reject conveyor positioned parallel to the infeed conveyor also from Roach. Pallet positioning If the information from the bar-code label is found by the PLC the controller then determines if a pallet already contains other cases with similar codes. The bar-code label also provides the PLC with case size pallet size and layer stacking information. The PLC communicates with the robot's ROBOTstar control system developed by Reis. Both are housed in a control cabinet adjacent to the robot. An Allen-Bradley 550 operator interface is also located at the cabinet. This allows Sandvik operators to start stop and adjust pick-and-place operations. The operator interface also permits operators to add modify or delete codes that are stored in the PLC's data table. If the PLC ascertains that the bar-code label information matches that of cases that have already been placed on a pallet it instructs the robot to pick up the case and transfer it to that pallet. If the case label doesn't match those of cases at any of six pallet zones or locations the PLC checks to determine if a proper pallet size is in position and ready for cases. If not the case is moved to the reject conveyor. When it's necessary to place a pallet in position to accept cases the operator shuts off an invisible light curtain system used to protect people from injury. Operators can move pallets into place or remove fully stacked pallets at any of the six pallet zones as well as refill the slipsheet hopper as needed. Precise placement of pallets is imperative to accurate case placement on the pallet by the robot. To achieve this placement the Reis system includes an L-shaped bracket mounted to the floor for each pallet zone. Forklift drivers must position the correct pallet size against the L. Placement is verified by two proximity sensors mounted to the floor behind each of the brackets to prevent them from damage. Slots cut into the brackets permit the sensors to look through the brackets and determine if the pallet is in place. Robotic controls The PLC and robotic controls system instruct the robot to pick up the case. The robotic head is capable of lifting 80 kg (176 lb) through vacuum. The gripper head is designed so that vacuum is delivered to three aluminum chambers. Each is further divided into two zones: one for the center chamber a second zone for the chambers to the left and right of center. For shorter cases vacuum is delivered only to the center zone; longer cases require vacuum at both zones. Once the gripper has picked up the case it elevates then traverses along a linear rail to the correct pallet position. By checking with a vacuum sensor the robot's software system makes a final check to make sure it hasn't dropped its payload. The system then calculates vectors within the ROBOTstar system and instructs the robot precisely where to place the case. At that point vacuum is released and the robot retracts returning to its home position for the next case. System advantages Presently Sandvik is operating the robot at about six/min speeds. "Speed was one of our concerns when we were considering the robot" admits Monyak. "Operators were very adept at palletizing but we went to Reis to test the robot's speed and it impressed us. It might take a little longer to do than it takes a person but the placement is better we have a nicer-looking pallet that's easier to stretch wrap and the robot doesn't have to take any breaks." "The Reis system also places a corrugated slip sheet [also from Stone Container] between every other row in certain packing patterns" says Clayton Arnold production manager. That too had been done manually. "We can also program the system to interlock boxes to stabilize loads" he adds. Before it selected the robotic system Sandvik investigated alternatives but the combination of advantages and price gave the nod to Reis. Monyak credits materials handling consulting firm CF Packaging Machinery (Greensboro NC) with recommending this system to Sandvik. The robotic system also provides Sandvik with advantages in tracking product. "In the past" says Monyak "we had to track each case manually and make sure we put it onto the proper pallet. That was so labor-intensive that we changed to putting different types of products and cases onto the same pallet. With the robotic system we're again separating them automatically." Also when Sandvik pulls capsules for random quality control checks if any capsule is found defective the case label information helps pinpoint the problem. That wasn't possible previously. And if a product was found to be unsatisfactory by a customer case label information could now be used to track the product back to the specific chub packaging machine even the shift and operator that filled the capsule. While Sandvik wouldn't reveal its volumes Monyak does say that the robotic system is capable of handling 5 cases per day-a number the company hopes to reach in the future. Plans also call for improving capsule filling speeds and automating case packing strapping and downstream stretch wrapping. In just the first month of operation at Sandvik's Bristol facility the robotic system has lived up to the company's expectations. "It wasn't easy to convince management to do this so we had to carefully justify the cost of the robotic system and weigh that against issues such as worker safety insurance concerns labor costs and operational speed" recalls Monyak. "With the savings we project we'll gain by using the system we anticipate a twenty-four-month payback and that was what our corporate team wanted in order to [sign off] on the project."

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