Simplifying, automating sortation system for recycling company
A recycling company hired a system integrator to automate a proprietary sortation system invented to aid recycling company customers with Leadership in Energy and Environmental Design (LEED) documentation.
- A recycling company looked to automate its process for delivering LEED results to their customers.
- Before this process, the sorting system was manual.
- Automation made the process more sustainable and efficient while giving the customers more accurate numbers.
System integration insights
- A recycling company looked to improve a motion control and documentation process invented for aiding customers in meeting documentation requirements for Leadership in Energy and Environmental Design (LEED) Certification.
- LEED Certification has many stringent requirements and that was a challenge for the recycling company because the information they had wasn’t always accurate.
- Automating the process provided the recycling company the ability to deliver more accurate results and simplified the process.
Richard S. Burns & Company Inc., a recycling company, handles more than 1500 tons a day of construction waste and materials and used motion controls and documentation to measure environmental improvements. They wanted to automate a brand-new process to aid customers in meeting documentation requirements for Leadership in Energy and Environmental Design (LEED) Certification.
The process involved a sortation system that required an automated lift and material tracking. The recycling company’s goals were to collect the weight of full individual bins of sorted commodities for each ticket, which in this case, summarizes the contents of a group of carts associated with an individual customer.
As the design development progressed, it became obvious that the system needed to be more automated. As the information technology (IT) software came into play and the complexity of the line grew, it was apparent that the line needed better and more accurate controls.
Prior to the invention of this system, the LEED reporting provided to its customers wasn’t as accurate, and the sortation was much more cumbersome. The on-site contractors would share dumpsters, and there was no way to determine what Company A or Company B recycled from the job. The recycling company was processing the dumpsters manually, sorting the materials into rolling bins, weighing them, and recording the data manually, leaving a lot of room for error.
The recycling company now has barcoded carts, giving them the ability to segregate what each company brought from the job site to the recycling facility. There are groups of 8 to 20 carts coming in from each customer. Individual carts have a barcode on them associated with a ticket. Each ticket is a group of carts assigned to a customer site. Each recycled commodity is weighed, and that data is reported back for each customer’s LEED documentation.
Project challenges: Automation, data collection, programming
The company had the capability to generate a ticket, pick up the carts, and bring them back. They needed automated controls to dump, photograph and weigh the materials. They also needed to tabulate the data by recycling material type, and communicate the data back into the company’s structured query language (SQL) database. The recycling company had its own engineers and IT experts that worked on this solution, but they didn’t have experience with programming industrial automation controls interfacing with digital electro-mechanical feedback devices such as encoders, and how to communicate the appropriate data collected back to the SQL database.
Before this system, the sortation process was often handled manually. There was a custom-written visual basic software program that was used to take pictures and catalog items, but the sorting process was manual. They had implemented the barcodes on the carts to associate the carts with the tickets, in terms of pickup, not in terms of processing and sorting.
Engineers had to anticipate the errors that could occur and then develop code to respond to specific errors that could happen. The engineers relied on experiences in interfacing with real-world problems and managing common problems in machine building to identify where potential issues could be and offer solutions from a controls perspective.
Improving the automation, communications process
The integrator recommended a programmable logic controller (PLC) for its communications capabilities and ability to integrate the various pieces of equipment. Having a more powerful PLC made the programming simpler, more concise, and easier to understand. The integrator team chose a PLC large enough to run two lines independently at the same time, knowing that in the future, the company would be adding a second line. A Microsoft Windows PC touchscreen human-machine interface (HMI) was implemented to allow operators to adjust the bins on the fly, based on the commodities that they have that day.
The customer already had the SQL database front end working, and the systems integrator added a predesigned SQL gateway module to interface with the SQL, which provided diagnostics. When a cart gets rolled into the system, it sends a query against the SQL database and looks for a ticket that contains that cart. The SQL database sends the cart information from the ticket to the PLC to process each cart in sequence. At the end of the process, the totals are tabulated and the ticket is completed. Weight information and pictures are sent back to the server, where the recycling company continues processing it for LEED documentation and customer billing.
Digital communications enable better diagnostics. If a load cell under a bin breaks using digital communications, it’s easy to pinpoint where the breakdown happened. If a scale failed, where it powered off or died using analog outputs and inputs, it might just show a weight of zero pounds. Using digital communications, if an error comes up, the HMI touchscreen says, “We lost communications with X device,” saying if and when there are problems, making diagnostics easier.
This system has 36 different devices “talking” over digital communications. The safety system is conveying the status of each input and output, each of the scales is communicating, the variable frequency drives (VFDs) that run the conveyors and hydraulics are communicating, and the barcode readers are communicating, in addition to SQL database communications.
The integrator also provided a barcode scanner, limit switches, proximity switches, and photo eye sensors to ensure everything is in the right place and lifting occurs correctly. Since the bins use hydraulics, the engineers determined they would need to add two outputs going to two hydraulic solenoid valves, two sensors on each bin, a push-button for the operator dump, and beacons to indicate the bins are full. All the dump stages had multiple input/output (I/O) devices, in addition to interlocking and safety-related items. Overall, the project required hundreds of I/O system inputs and outputs.
For the visual element, the integrator installed and integrated high-resolution cameras using trigger outputs from the PLC to signal image capture, and then automatically writing back to a file storage server associated with the ticket. To keep the camera and barcode reader clean and able to read, a water spraying dust mitigation system was integrated by putting in the controls to cycle on and off based on the distance from the time the cart was dumped. The PLC triggers the spray as needed to keep the lenses clean.
The original hydraulic conveyor couldn’t provide the speed and torque that was needed, so the integrator converted the conveyor to an electrical system. The team added encoders that track belt positions to gain visibility into how far a product has traveled at any given time. With the encoders on both conveyors, there is feedback, a functional safety system of rope pulls, and an elaborate one-wire safety system.
This is a safety integrity level (SIL3) PLe system, nearly the top level of safety requirements. It is a measure of safety system performance, in terms of the probability of failure on demand (PFD). The higher the SIL, the lower the risk of a dangerous failure. The major hazard in this system is the lift. It’s capable of lifting thousands of pounds. A guard door prevents access to it with magnetic locks and other safety sensors to ensure it doesn’t get opened during operation. Various e-stops are located around the system. Rope pull safety switches for the operators at the conveyor, controlled by a separate safety processor. The safety processor communicates the status of each sensor with the PLC, so if something goes wrong, the PLC would shut things down and trigger an HMI alarm.
The integrator team anticipated having to mitigate many potential real-world issues in the programming code sequences during the development phase after they built the panel in their shop.
For example, if a cart is too heavy to lift, the system is programmed to record the weight without dumping it and add the weight to the total commodity weight returning to the SQL system. In another example, if a cart is full of only drywall, the operator can use the HMI to say, “all of the material is drywall,” and that cart’s weight gets added to that commodity. Each motion-control application challenge was met with a solution and programmed into the system.
Dave Curry, an IT engineer from the recycling company said, “The software that they wrote for the panel is spot on. We don’t have bugs; it is very, very reliable.”
Another real-world issue was the “missing cart” factor. Loading docks and staging areas often have hundreds of carts, sometimes stacked two or three deep. The beginning of this process is still manual, and if an operator is looking for a cart for ticket X, and it’s stuck behind a cart for ticket Y, the cart may be delayed. Programming processes a partial ticket containing only uncompleted carts. It was a team effort to get this done. The recycling company’s engineers had to reprogram their side of the system to handle partial tickets, and the integrator had to handle the partial tickets coming back.
Motion controls for the lift needed adjustment. Issues had occurred during colder months where materials would freeze or stick to the bottom of the carts. The sequence had to be modified to jiggle the carts to loosen the items. The PLC was programmed to command the hydraulics to rotate back and forth a few times. The first time a cart rolls in, it does a normal rotation to dump and then rotates back, but if the same cart is rolled in a second time, it automatically considers it a re-dump.
If the cart comes back down on the lift, a scale under the lift can detect if there’s still weight in the cart. If that is the case, it prompts the operator via the HMI to engage the re-dump button to shake the cart a second time. The operator also can manually loosen items and then resend the cart to dump.
Benefits of automated motion control, documentation
With the increasing emphasis on sustainability and recycling, this system helps companies meet and document LEED Certification requirements. Automating portions of this process makes it more sustainable and efficient. Ultimately this innovative solution costs less because it removes much of the manual process and is more accurate in reporting than manually sorting materials.
Nathan Ferrin is controls specialist at Cornerstone Automation, which is a member of the Control System Integrators Association (CSIA). CSIA is a CFE Media and Technology content partner. Edited by Chris Vavra, web content manager, CFE Media and Technology, firstname.lastname@example.org.
Keywords: automation, bin-picking, motion control, system integration
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Original content can be found at Control Engineering.