Checkweighing machines are used for the principal purpose of checking the weight of products once they have been packaged. The checkweighing machine is programmed to identify whether the product fits within specified weight limits. Where a product fails to weigh within these limits, a reject mechanism is triggered, causing the product to be diverted along a separate conveyor belt to be dealt with appropriately.
An automatic checkweigher system comprises a series of conveyor belts, typically three, including:
- Infeed Belt: Changes speed of package to that required for weighing and can also set the gap between products (indexer). An infeed belt can also incorporate additional belts or change for the purpose of positioning product correctly for weighing.
- Weigh Belt: Mounted on top of a weight transducer, the weigh belt is - as the name suggests - the part of the checkweigher machine system that measures the weight of the product.
- Reject Belt: For products that do not fit within the weight parameters set, the reject belt re-routes the product to be dealt with. The method of rejection varies depending on the product. For example, some work using air-amplifiers whilst others use a linear or radial actuator.
Checkweigher scales are extremely important in Packaging, particularly in the food industry. The need for products to be accurately weighed and labelled is directly proportional to the price paid by the end user, so the checkweigher must be calibrated as accurately as possible.
Some products require high-precision weighing, for which it is often necessary to incorporate electromagnetic force restoration, strain gauges or vibrating wire load cells. It is also necessary for the checkweigher system to incorporate functionality to exclude extraneous factors that may adversely affect the accuracy of the reading (for example, from draughts caused by air-conditioning or refrigeration units).
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Many wholesalers demand accurate weight checks on products to ensure that customers are being appropriately charged for the volume of product they purchase. There can be large fines payable by the packaging company for inaccurately weighing products.
As technology has advanced, more sophisticated checkweigher systems have become available. Checkweighers can now incorporate communicative functionality that allows the weigher to integrate with other sections of the production line to ensure weight control is adhered to throughout the line. Data collection has also become easier as a result of improved connectivity along the production line. Data on pack weights, as well as statistics from across the line flow, can be recorded and used to further streamline and optimise performance.
Types of Checkweighing Machines
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- Load cell
- Belt weigher system
- Inline checkweigher
- Strain gauge
- Filter simulation
- Reject mechanism
- In-motion scales
- Conveyor scales
- Dynamic scales
- Inline scales
- Weight transducer
- Servo-balance (Force-balance)
- Split beam
- Electromagnetic force restoration
- Weigh bed
- Vibrating wire
- Pneumatic pusher
- Diverting arm
- Zone checkweigher
- Open flap detection
- Bar-code scanner
- Temperature sensor
- Vision inspector
- Timing screw
- Indexing gates
- Concentrator ducts