An automatic bagging machine controls single-bag weight mainly through closed-loop weight feedback control. The machine collects net weight data in real time, adjusts the feeding rate and feed amount dynamically, and coordinates the discharge sequence. General industry accuracy can be kept within ±0.3% to ±1%. If non-standard parts such as weighing platforms, feeding valves, or screw conveyor connectors need to be modified for the site, we can custom machine them according to customer drawings. Hansheng Automation supports single-piece and small-batch delivery.
Staged feeding control logic
- Most automatic bagging machines use net weight weighing control. They directly collect the real-time weight of the material in the bag to avoid errors caused by tare weight fluctuation. Feeding is divided into two stages.
- Coarse feeding stage: the machine feeds material into the bag at the maximum rated conveying rate. When the cumulative weight collected by the load cell reaches 85% to 95% of the target weight, the machine automatically switches to fine feeding mode to avoid overfilling caused by full-speed feeding. For high-precision industries such as food and pharmaceuticals, the trigger threshold can be set to 90% to 95% to further reduce deviation.
- Fine feeding stage: the machine supplements material at a very low feeding rate. It compares the weighing data with the target value in real time, gradually fine-tunes the feed amount, and stops feeding immediately when the preset weight threshold is reached.
- Closed-loop feedback adjustment mechanism
- The system uses a PID closed-loop adjustment algorithm. Real-time weight data from the load cell is sent to an industrial PLC or embedded industrial computer. The system calculates the difference from the preset target weight and dynamically adjusts operating parameters of the actuators, such as the speed of the variable-frequency feeding motor or the opening of the pneumatic feeding valve.
- For materials that tend to cake or have poor flowability, a vibration-assisted feeding device can be added. It works with closed-loop adjustment to avoid underfilling.
- Key hardware and calibration requirements
- Core hardware components
Load cell: use a strain gauge load cell of C3 class or above that meets OIML R60, with a sampling frequency of no less than 100 Hz, to ensure real-time and accurate data collection. Install damping pads on the weighing platform to offset weighing interference from workshop equipment vibration.
Actuators: for powder materials, use a pneumatic butterfly valve with a screw feeder. For granular materials, use a variable-frequency belt conveyor to achieve precise feeding rate adjustment.
Control unit: use an industrial PLC as the core control unit, with an independent weight adjustment subroutine to avoid conflicts with other equipment control logic.
Regular calibration process
Every 100 to 500 bags, use standard weights to perform zero calibration and span calibration on the load cell. At the same time, spot-check single-bag weights and correct PID adjustment parameters to offset equipment wear and sensor drift errors from long-term operation.
- Weight control in the discharge stage
- When the weight reaches the target, the discharge cylinder is triggered to open the discharge door, and the discharge timer starts. The discharge door is closed only after the material has fully entered the bag, to prevent residual material from affecting the next bag's filling weight.
- For overfilled or underfilled bags, an automatic weighing rejection device can be added to sort nonconforming products to a dedicated recovery area, preventing them from entering downstream processes.
Our custom precision parts machining capability is not limited to automatic bagging machines. In addition to parts for food packaging machinery, pharmaceutical packaging equipment, and powder conveying equipment, Hansheng Automation can machine yacht precision parts, RC car precision parts, tobacco packaging machinery parts, and filling machinery parts according to drawings. We also machine non-standard parts for printing machinery and medical devices, supporting drawing-based customization and small-batch delivery.
