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A production machine or system sitting on the plant floor can seem so reliable, so second nature, that it can be taken for granted. It’s easy to overlook how it actually solves a problem, or how it might be improved upon to solve future problems. Computerized combination weighers represent such an example. They may seem to be black boxes, calculating massive amounts of product weights and popping out perfect packages.
Simply defined, a combination weigher is a machine with several hoppers (or buckets or heads) that hold a known portion of the finished product. They discharged their contents into a final package in just the right combination to provide a desired net weight.
Aside from incremental advances in sanitary quick-disconnects, actuators, stepper motors and microprocessors, these machines’ basic technology hasn’t changed since the early 1980s, when they bowed in the marketplace. But there are still many smaller plants that use labor-intensive manual operations or even automated volumetric or net-weight systems that the larger food processors have left behind.
“Before combination weighers, volumetric or single-fill type machinery would stop filling when it got up to just under the right weight — that’s when you stopped feeding,” says Steve Bergholt, chief engineer for Triangle Package Machinery Co., Chicago. “You just had to hope it filled up to the right weight.”
For packages consisting of pieces this was a slow and inaccurate solution, and prone to lost profits due to product give-away. Consider how eight 2-oz. drumsticks can complete a 16-oz. tray pack, but if one is a fraction underweight, it will take a whole, ninth drumstick to complete the package.
In contrast, combination weighers combine, for example, heavy and light drumsticks, or any product that’s packaged in pieces. While the technology is well established, it still takes some specialized knowledge and expertise to ensure that the product is gently and efficiently guided through infeed, weighting and discharge sections.Versatile configurations
The possibilities for engineering a weighing solution are nearly endless. There’s no single solution for a single application, such as filling the multiple sections in a prepared “TV dinner”-type meal.
“This can be done in a few different ways, starting with a multi-product, multi-outlet type of configuration,” says Brian Barr, sales manager for Heat and Control Inc.’s packaging systems division, Hayward, Calif., which includes the Ishida combination weigher line. For example, buckets and discharges can be divided into two or three sections, so one machine can fill a separate protein, vegetable and starch into a single tray.
In addition to weighing a single product, combination scales like this Ishida model can blend and weigh multiple products.
Barr says this may or may not be the desired configuration, depending upon a customer’s line and speed requirements, because three weighers can also be used in a “single product, single outlet” mode, one for each meal component, for higher throughput. Additionally, he explains, a “multi-product, single outlet” configuration is typically the choice for blending products, where the net package is a mixture, such as mixed nuts. The buckets do the weighing for multiple types of nuts, and the mixing occurs at the discharge.
Multiple discharges are one of food processors’ favorite tricks, says Triangle’s Bergholt. “You can take four of your 18 buckets that have known weights in them, and use those four to make up a good package. And out of the remaining 14, you have the machine pick another good combination from four different buckets at the same time. That way you can make discharges twice as fast as you have to weigh and refill those buckets.”
The combinations are seemingly endless, if not infinite. On a machine with six weigh buckets above combining into 12 chambers below, there are a mere 4,096 possible combinations. Compared that to one with nine weigh buckets above feeding 18 chambers, which has a quarter-million possible combinations, according to Bergholt.
“More combinations usually translate into a better chance of achieving the perfect package weight,” he says, regardless of whether the design is radial or in-line. Of course, every application is unique to the food product, plant and business objectives of the company running it.Broad applications
Applications vary as widely as the mathematical combinations behind those buckets. Anything weighed and packaged in pieces seems to be fair game: fruits and vegetables; snack seeds, nuts and chips; candy and candy bars; cereals from bagged rice and grains; and wet, sticky meats and poultry.
“And you’d be surprised how much beef jerky sold every day that comes of our weighers,” says Anthony Delviscio, president of CombiScale Inc., Elk Grove Village, Ill. He notes those machines typically run 120 packages a minute using 14-head machines.
While he says the price on the first generation of machines may have been too high for “mom and pop” shops, the market for combination units has exploded with competition. Combi, for example, offers larger units as well as an inexpensive eight-head machine for small to medium food processing lines. “In the past, there was a tremendous jump in price from a volumetric system to a combination weigher,” says Delviscio. “It could be the difference between a $20,000 system or one over $100,000. Now we can offer the same system for $40,000.”
While more buckets translates to more speed, the low-end system still offers value, he says. “We can save processors money by packaging more accurately, minimizing their giveaway and lessening their investment into this technology."
As with throughput, the ideal size, number and shape of buckets vary with the size of pieces being packed, the final package’s net weight and other factors. A machine with the same number of buckets and discharge hoppers below might bag 170 small bags of hard candy, 100 1-lb. bags of rice or 30 8-oz bags of frozen chicken nuggets per minute.
Production needs also dictate the best solution. For example, radial designs are the nearly universal choice for all products. They are adaptable for larger products because it’s easier to fit them with bigger buckets.
But in some cases, users may also consider a linear design. A free-flowing product like cereal may lend itself to an in-line weigher’s smaller floor-space footprint and ease of retrofitting a cover to collect the dust that kicks up in such applications. And while vibratory infeed conveyors may be most common, a sticky product such as raw meat may require a conveyor that may be more easily installed below an inline unit. Below are some additional application considerations:
- Sticky, meat and poultry: Raw, marinated or otherwise wet and sticky products such as chicken tenders and other meats, as well as some fruits and vegetables, can present some of the greatest challenges. They can cling to vibratory conveyors, necessitating dimpled or embossed metal surfaces to minimize the surface area of product contact. Belt instead of vibratory conveyors may be used, and water sprays can keep sticky product moving.
- Fragile products: You must “handle with care” products that can break, such as bakery products — think mini-muffins and mini-doughnuts that are bagged. “For applications like these, we have gentle handling solutions,” says Heat and Control’s Barr. “We generally try to make sure each transition from hopper to hopper is very gentle and gradual. We can reduce the slopes or angles, and minimize drop distances to avoid any degradation of the product while you're feeding it through the system.”
- Temperature extremes: High heats can cause oils and greases to build up, particularly for deep-fried foods. The solution comes with more frequent washdowns and cleanings. Air conditioning units may be used to cool control cabinets. In freezing environments, washdown presents its own problem: freezing. Some processors may cycle their machines “dry” until they’re ready to run product in order to prevent machines from freezing and seizing.
- Fine grains: Tight-closing “sift-proof hoppers,” as Ishida calls them, ensure that fines don’t get through the hopper openings when in the closed position.
There’s a learning curve to adopting new technology, even for what might appear to be a simple machine. Simply put, replacing a slow, old machine with a new one that runs twice as fast “doesn't mean you can use your old packaging materials. You can't just buy a faster machine and have it magically make everything faster,” Triangle’s Bergholt says, noting that an old set of packaging jaws may need more dwell time.
Both the supplier and the food processor share the responsibility to ensure such issues are addressed long before a purchase is made and that the solution meets application requirements.
This is often alleviated by the nature of the supplier or OEM; many offer services and equipment for both mechanical and electronic integration to upstream and downstream product handling, processing and packaging components.
And while the heart of the high-speed logic that controls weight combinations is proprietary, vendors are increasingly offering connectivity features and services to help processors transfer and access data through Windows interfaces and Ethernet connections, which are but two of the standards food processors expect.