An eye on vision systems
“As machine vision technology has become more rigorous it has become more successful in addressing applications in the food industry,” says Nello Zuech, a consultant to the vision industry and contributor to www.machinevisiononline.org
“While there are many applications of machine vision in the packaging side of the food industry [newer] applications include sorting and grading,” he continues. “With advances in color cameras and the underlying ability of microprocessors to handle the additional data derived from color-based processing, more applications are being addressed. In some cases multispectral processing is now possible at the speeds required to keep up with processing tons of a product per hour.”
|Inspection is a key job for vision systems in the food industry. A Cognex vision system inspects bottle caps at Original Juice Co.
Original Juice Co., Northgate, Australia, wanted assurance that every cap on its bottles was applied fully, straight and not skewed, and that the tamper-band is not broken. The company wanted a vision system that could inspect a variety of imperfections not tolerated on high-speed lines and filling equipment.
In addition to being reliable and repetitive, the vision system would need to inspect at speeds of up to 300 bottles per minute. The In-Sight 5100 from Cognex (www.cognex.com
), Natick, Mass., incorporates a die-cast aluminum housing and sealed industrial M12 connectors to achieve an IP-67 rating for dust and wash-down protection on the factory floor. These environmental attributes would prove to be crucial in withstanding the wet, citric-acid environment of the inspection site.
The overall system consists of a touch-screen industrial PC incorporated into a stainless steel enclosure. The enclosure also houses the Ethernet hub, the digital power supply of the lights, a PLC and various power distribution components. After bottles have been filled and capped they travel down the conveyor line, where two cameras sequentially inspect the bottles.
The first camera looks directly at one side of the bottle and inspects the bottle cap at this side only. A red LED backlight provides the camera with a silhouette image of the bottle. Back lighting provides maximum contrast between the product outline and its background and is ideal for measuring external part edges. This results in images that work extremely well for the vision sensor's measurement and inspection tools.
When the bottle comes within the camera's field of view, a sensor is triggered and an image is taken. Cognex In-Sight vision software tools then analyze the image for defects and determine whether a bottle is flawed or not. In the event of a failure being detected, a fail signal is sent via one of the camera's outputs to the PLC. The PLC then triggers a reject mechanism, which removes the bottle from the line. After passing the first camera, the bottle will travel a little further before the second camera acquires another image of it, performing the same inspection on the other side of the bottle cap.Labor vs. machine: the payback drama continues
The high capital outlay required for highly automated systems poses a perpetual challenge of cost justification, particularly when important issues like job displacement are drawn to the fore. The makers of automation equipment claim that, in general, European companies are quicker to recognize the return on investment than American processors.
"We make a continuing effort to lower the cost of the equipment we bring to the market," says ABB's Smith, pointing to the improved costs of drives and lowered cost of manufacturing. "Look at a robot in the 1980s. The cost today is half what it was then. A $110,000 robot in the 1980s costs about $55,000 to $60,000 today. We have had to reduce our costs to stay competitive and to be available to all companies."
Improved software has greatly simplified robotics usage, she adds. "Now we have structured packages that make it much easier to develop a program." A software package called "Robot Studio" enables processors to develop production programs completely off-line. Changeover is often simple and quick, even when it involves significantly different products. "Often it is just a matter of changing software, or changing software and a gripper (flexible hand)," she says. Cost savings: a practical matter
Today's processors are at their most practical where cost savings is concerned.
Today's automation helps control waste, ingredient usage, and energy utilization and enables real-time inventory tracking. System-wide monitoring and control is possible with Ethernet LANs. Communications networking
At a major milk-drying factory in Ontario, systems provided by Tetra Pak (www.tetrapakprocessing.com
) allow control of process valves, temperature and other processing variables through a DeviceNet network. DeviceNet, a simple and low-cost communications standard for connecting industrial devices, “allows better control of the processes and allows quick modifications and expansions during the life-cycle of the factory," says Axel Andersson, manager of automation engineering for Tetra Pak, based in Vernon Hills, Ill.
"Equipment like valves and pumps can be controlled," says Andersson. "You can monitor the strokes of pumps. You can also use the systems for predictive maintenance."
While control of the processes is the main consideration, an increasingly important side-benefit is energy savings, a huge consideration in today's world business climate. Variable frequency drives, for example, are programmed to keep energy use to a minimum without sacrificing optimum processing.
Such oversight control can help reduce other types of waste as well. Jean Pierre Berlan, sales director for the Tetra Pak processing division, notes that careful monitoring of milk flow with turbidity meters following the cleaning cycle in a milk operation can deliver significant savings. "The turbidity meter lets you know where the mix [of water with milk] begins and ends so that you can at the same time secure the best product quality and optimize product losses, says Berlan.
"The dairy industry still is very conservative and the vast majority of the dairy facilities still use a timer when they flush their pipes. They are not optimizing the product recovery," continues Berlan. "The evolution of sensors is enabling us to optimize a factory far better than we could 10 to 15 years ago."A Florida citrus processing plant demonstrates how enterprise resource planning (ERP) can be effected using PLC-networked systems over an Ethernet local-area network (LAN). The end result is considerable inventory reduction.
"You can manage your business from a central control station," explains Charles Matthews at Florida's Natural Growers in Lake Wales, Fla. Florida's Natural upgraded its processing system several years ago. "And we have been constantly adding to it since," says Matthews. The ERP system is gathering critical and timely plant information that assists with planning, ordering and cost control.
"In the southern U.S., we commissioned this year a complete dairy plant where the process control is connected to the ERP system," says Tetra Pak's Berlan. "This type of set-up allows for a real-time update of production, facilitating inventory management for both raw materials and finished goods."
"To plan as accurately as possible, you need accurate information," adds Andersson.
The systems can monitor the entry of ingredients onto the process lines and provide immediate inventory and usage updates. "The ERP system will deduct ingredient taken from inventory," notes Berlan. "If you have accurate information exchange, you don't need as large a threshold of stock. Yes, you can get the information in other ways, but that is an open door to human error."