Gravimix doses all components gravimetrically (by weight). As a result, fluctuations in bulk density, changes in particle size or differences in flow behavior do not affect dosing accuracy. Because the system calibrates itself, no sample dosing is needed for a new material; for a color or material change the unit can be dismantled and cleaned without tools.
Total dosing accuracy reaches up to ± 0.1% — and this also holds for small quantities and demanding dosing conditions. With up to 10 stations a capacity of 2,500 kg/h is reached; up to four stations (up to eight on large systems) use slide valves for free-flowing components, and one or two precision screw feeders can be added for small quantities of additives.
The following steps are the normal start-up sequence of the system. An emergency stop is performed by switching the machine off with the main switch on the control box.
From then on, the machine runs automatically according to the recipe you created.
The controller describes the state of the machine with the following headings:
| State | Description |
|---|---|
| Idle | At power-up the controller is in this state if it finds no recipe. The machine will not start until a recipe is entered. |
| Standby | The machine is fully at rest but can be started at any moment. In this state a recipe, parameters and commands can be sent. |
| Profibus | The machine is managed through a SCADA package or a PLC. The handheld terminal is for monitoring only; local control returns when Profibus control is released. |
| Operating | A blend is being produced according to the selected recipe. |
| Stop requested | A stop command was received; the machine will finish the running batch cycle and then stop. If a start command is given meanwhile, it returns to production. |
| Error | An error was detected and the system stopped. The error is shown on screen; once cleared, it is reset by acknowledging it. |
Gravimix can be operated with an industrial PC, with the handheld terminal or with a combination of both. To prevent several controllers from conflicting, the mode is selected under Menu → Interface → System. In Local mode a new recipe can be created on the handheld terminal (in combined operation this recipe is stored as recipe number 0 on the central controller). In Remote mode the central controller sends the recipes; only the percentages can be changed on the handheld terminal.
| Mode | Description |
|---|---|
| Gravimetric | Each component is dosed and weighed separately. Highest accuracy; longer cycle time, lower capacity. |
| Volumetric | All components are dosed simultaneously according to the dosing times calculated by the system and discharged directly into the mixing chamber. No weighing takes place — lower accuracy, highest capacity. |
| Combination | One gravimetric dosing is followed by a defined number of volumetric dosings (combinationRatio; e.g. 1:3). It combines gravimetric accuracy with volumetric speed. If the mixing chamber is full, the system automatically doses gravimetrically instead of volumetrically. |
| Production Mode | Behavior |
|---|---|
| Continue | After the start command, production does not stop by itself; it continues until the material runs out or an error occurs. |
| Alarm-Weight | A target weight is entered. When the produced weight reaches or exceeds the target, an alarm goes to the operator, but production continues. The alarm is cleared by resetting the produced weight on the "Totals" screen. |
| Weight → Error | When the target weight is reached an error is generated and production stops. |
| Mixer Mode | Behavior |
|---|---|
| Normal | The mixer is off during production. When material is discharged from the weigh bin, it runs for the mixerOnTime period. |
| Pulsing | The mixer runs in pulses during production; the on and off times are set with mixerPulseOnTime / mixerPulseOffTime. |
| Off | The mixer is always off. |
| On | The mixer runs continuously during production. |
The recipe is the core of the controller; the material to be produced is defined here (Menu → Recipe). At most 6 hopper input fields are visible on the screen at once; depending on the machine configuration up to 10 hoppers can be shown. The dosing order is changed by selecting a hopper and moving it up or down with the arrow keys.
| Field | Value | Meaning |
|---|---|---|
| TYPE | REG, NAT, ADD | Type of material in the hopper: Regrind, Natural, Additive. |
| ALARM | IGNORE, WARN, FAILURE | Alarm type for the hopper concerned. |
| GR/S | g/s | Discharge rate of the material in the hopper. |
| GR/PLS | g/pulse | Discharge rate in pulse dosing. |
The components are defined as follows: REG as a percentage of the batch weight, NAT as a ratio to the other natural components, ADD as a percentage of the total of all naturals.
In this method the REG, NAT and ADD values are all direct percentages of the batch weight. The total must be exactly 100%.
Every mechanical valve has a reaction time. The controller calculates how long the valve stays open using the Hardware Reaction Time and works in 5 ms pulses:
After the first dosing, the dosing rate is recalculated from the measured weight. The correction is applied if the deviation is within the dispenseRateVarBand limit — this prevents the controller from calculating a wrong value when the hopper runs empty:
When the dosing stays below target, the controller behaves according to the alarm type selected in the recipe: IGNORE makes no further attempt and corrects by recalculating the ratios; WARNING makes additional attempts up to the dispenseTry count and, if the accuracy is not reached, only warns and moves on to the next material; ERROR gives an error and waits for a start command for new dosing attempts until the accuracy is achieved. Overdosing cannot be corrected; only the ratios within the recipe are recalculated.
To determine the weight from the load cell signal, the controller calculates a weight line through two points. These two points are entered under Menu → Calibrate → Calibrate, and both steps must be carried out:
External influences, temperature, aging or overloading can shift the weight line of the weigh bin. The operator notices this from the deviation in zero weight while the machine is in standby. Since the weight line itself is correct and only its starting point has shifted, no full recalibration is needed — a tare is taken with Menu → Calibration → Tarration and the display returns to approximately 0 grams.
If the mechanical delay of the valves and screws is not added to the calculated time, serious dosing deviation results. The comparison below shows this (assuming 6 pulses = 30 ms):
| Dosing | Rate | Target | Time | Actual | Deviation |
|---|---|---|---|---|---|
| Reaction time not taken into account | |||||
| Screw | 7 g/s | 14 g | 1.97 s | 13.79 g | 1.5% |
| Valve | 800 g/s | 600 g | 0.72 s | 576 g | 4% |
| Reaction time added | |||||
| Screw | 7 g/s | 14 g | 1.97 + 0.03 = 2 s | 14 g | 0% |
| Valve | 800 g/s | 600 g | 0.72 + 0.03 = 0.75 s | 600 g | 0% |
The values are set under Menu → Calibrate → Hardware reaction time. F (factor) is the minimum opening time for dosing; if the calculated time is shorter than factor × pulse time, the machine uses this value. If you get the "hopper is empty" alarm even though the hopper is full, increase the factor (maximum 10). P expresses the reaction time in pulses of 0.005 seconds, T in seconds.
For small quantities the machine automatically switches to pulse dosing. Pulsing is used for dosing quantities below W[g]. To set it, close the weigh bin, note the current weight, select the hopper you want to test and apply a single pulse with test pulse time, then measure the weight increase. On time (0.010 – 0.040 s) is increased or decreased to adjust the amount of material falling from the hopper; Off time (0.050 – 0.300 s) gives the material time to fall from the slide and should not be too short. Pulse dosing comes at the expense of maximum capacity.
The parameters fall into two groups: general parameters can be changed by the operator, protected parameters only with a password.
| Parameter | Description | Default |
|---|---|---|
| ProductionMode | Production mode: CONTINUE, WEIGHT or ALARM_WEIGHT. If WEIGHT/ALARM_WEIGHT is selected, productionWeight must also be entered. | CONTINUE |
| ProductionWeight | Production stops when this weight is reached (mode must be WEIGHT or ALARM_WEIGHT). | 100 kg |
| DispenseMode | Dosing mode: GRAVIMETRIC, VOLUMETRIC or COMBINATION. If COMBINATION is selected, combinationRatio must be entered. | GRAVIMETRIC |
| CombinationRatio | Ratio of volumetric to gravimetric dosing (one gravimetric + x volumetric). | 3 |
| WeighbinDumpTime | Time the weigh bin stays open while the material is discharged into the mixing chamber. | 5 s |
| LevelControlWaitTime | Time between the mixing chamber full signal and the opening of the discharge valve. | 8 s |
| LevelControlDumpTime | Time the discharge valve stays open after the sensor is uncovered. | 1 s |
| MixMode | Mixer mode: ON, OFF, NORMAL or PULSE. | PULSE |
| MixerOnTime | In normal mode, the mixer running time after the material has been discharged. | 10 s |
| MixerPulseOnTime | Mixer on time in pulsing mode. | 2 s |
| MixerPulseOffTime | Mixer off time in pulsing mode. | 15 s |
| Parameter | Description | Default |
|---|---|---|
| DispenseTries | Maximum number of attempts to reach the target accuracy for a component. | 4 |
| DispenseAccuracy | Minimum accuracy for each component. | 15 % |
| DispenseCorrectionBand | Maximum deviation allowed when the dosing rate is recalculated. | 20 % |
| Batch Weight | Total weight of all dosed components. | — |
| Loadcell Range | Maximum weight in the weigh bin; if exceeded, the controller gives an error. | Depends on type |
| Maximum tara variation | Permitted absolute deviation of the weigh bin zero point. | 40 g |
| Alarm on overdosing | An alarm is generated when a component is overdosed. | No |
| Weight in | Weight unit: kilogram/gram or pound/ounce. | kg – g |
| Dispense Guard | Monitors the discharged weight of the component during dosing. | Recipe change |
| Maximum Hoppers | Number of hoppers on the machine. | 1 – 10 |
| Weight settle time | Time waited between dosing and weighing for the bin to settle. | 1.0 s |
| Weight variation band | Band within which the upper weighings must stay relative to the average weight. | 2 g |
| Make recipe adaptive | In percentage mode, adapts the components to the first one dosed. | Yes |
| Infinite dosage retry | Keeps retrying the dosing indefinitely while the hopper is empty. | No |
| Autostart production | Starting production with a separate button (option). | No |
| Weighbin clatter cycles | Opening and closing the weigh bin flap before dosing starts. | No |
| CSV Batch report | Starts saving the usage data report. | No |
| CSV Clear after copy | Renews the CSV file after copying. | No |
The maximum weight in the weigh bin depends on the Gravimix type:
| Unit | Max. Weight | Model |
|---|---|---|
| 0.5 kg unit | 0.8 kg | FGB-MINI and FGB MECS |
| 1 kg unit | 1.2 kg | FGB-1 |
| 1.5 kg unit | 2.0 kg | FGB-1.5 and FGB FLECS |
| 2 kg unit | 3.0 kg | FGB-2 |
| 5 kg unit | 6.0 kg | FGB-5 |
| 10 kg unit | 12.0 kg | FGB-10 |
| 25 kg unit | 30.0 kg | FGB-25 |
To record production data automatically, a formatted SD card must be in the SD slot on the controller board; all usage data and alarms are written to it continuously. In the protected parameters, set CSV batchreport → Yes. When a memory stick is inserted into the USB port on the control panel, the data is copied from the SD card to the stick; the alarm lamp flashes during copying and goes out when copying is complete. If the CSV reset after copy parameter is no, the file is kept; if it is yes, a new file is created. The file name has the format BRxx.ddmmyy; xx is the node number set with the DIP switches on the blender's PCB.
When an error is detected, the controller sends the message to the user interface; messages are recorded in the alarm history with date and time.
| Alarm Message | Meaning | Solution |
|---|---|---|
| Press recover | The alarm has already been reported and only needs to be acknowledged. | Press the button to acknowledge. |
| No control voltage | There is no control voltage. | Switch on the control voltage and acknowledge. |
| Panels are open | The front panel has been removed or the mixing chamber is not fitted. | Refit the protective cover and/or the mixing chamber and acknowledge. |
| Production weight reached | The set production weight has been reached. | Reset the produced weight on the "Totals" screen. |
| Parameters are corrupted | The check number of the stored parameters is incorrect; all parameters have returned to default. | Information message only — acknowledge, then review the parameters. |
| Production data corrupted | The check number of the stored production data is incorrect; the data has been reset. | Information message only — acknowledge. |
| Loadcell is not calibrated | The stored load cell parameters are incorrect. | Calibrate the weigh bin. |
| Loadcell overload | The weight in the weigh bin exceeds the set "load cell overload" value. | Discharge the excess material and acknowledge. |
| Loadcell not stable | The weight in the weigh bin does not settle into the stable band within the specified time. | Acknowledge. If it recurs often: the weigh bin dump time may be too short, the mixing chamber may be overfilled or material may be sticking to the bin flap. The sensor in the mixing chamber should be moved down or the batch weight reduced. |
| Weighbin out of tare-band | The zero weight of the weigh bin has deviated by more than the "maximum tare variation" value. | Tare or recalibrate the weigh bin. |
| Connection with FGB broken | There is no communication between the controller and the machine. | Check the cable and its connections. |
| Silo full error | The storage silo stayed full for the set number of batches (upper level sensor active). | Regrind consumption is too low — increase the ratio or feed less. |
| Silo empty error | The storage silo stayed empty for the set number of batches (lower level sensor not active). | Regrind consumption is too high — reduce the ratio or feed more. |
| Low level in hopper | The optional sensor detected that the hopper is about to run empty. | Fill the hopper. |
| Hopper is empty | The controller detected from a very low dosing that the hopper is empty. | Fill the hopper and start the machine. If this alarm appears while the hopper is full: the dosing accuracy may be too tight, the dosing rate too high or the number of attempts too low. |
| Hopper is overdosing | An alarm was generated after overdosing. | Depends on the component — review the dosing rate and accuracy settings. |
| Emergency stop executed | The stop button was pressed twice and an emergency stop was performed. | Acknowledge. |
The unit is adjusted and tested at the factory; adjustments should only be made if one of the following does not work properly.
Approximately 6 bar for the best result. The blender also works at lower pressure — minimum 4 bar.
The sensor should protrude approximately 10 mm into the mixing chamber. If it protrudes too far it detects the mixer blades; too little and it detects the mounting plate instead of the material (FGB-10 and FGB-25 differ). The sensitivity is adjusted with the small screw inside the sensor:
The valve should close quietly. There is an air flow control valve on the leftmost pneumatic valve; it is adjusted with the screw on top (on the FGB-MINI the control valve is on the cylinder of the weigh bin).
The cleaning frequency depends on the number of raw material changes. The hoppers are emptied from the Menu → Cleaning menu; a single hopper or the other parts can be operated independently. The machine can only be cleaned in standby and with the control voltage switched on; in addition, the mixing chamber must be fitted and the front panel closed (a discharge funnel can also be used instead of the front panel). For cleaning, the front panel, weigh bin, mixing chamber and mixer are removed. The solenoid valves and compressed air must be off; clean with a vacuum cleaner and wear safety glasses.
Before the blender is moved, the weigh bin must be removed — otherwise the load cells will be damaged. The unit can then be transported on a sturdy pallet.
FGB 5 / 10 / 25 series: 240 V 50/60 Hz (P+N+PE) and 400 V 50/60 Hz (3P+N+PE) supply; clean, dry compressed air at a constant pressure of minimum 6 bar, ¼" BSP connection.
FGB MECS and FGB FLECS: 240 V 50/60 Hz (P+N+PE) supply; same air requirements.
The blender can be mounted on a stand with an integrated vacuum discharge box, on a platform or frame above the processing machine, or directly on the processing machine. It is fixed with the mounting holes in the base plate.
Once installation is complete, the mixer, mixing chamber and weigh bin are fitted and the front panel is closed. The compressed air is connected to the pressure regulator (max. 12 bar). The supply voltage must be "clean" in terms of fluctuation and interference. The communication cable (especially RS-422) must not run in the same duct as cables carrying high current — induction interference will occur. Because of load cell accuracy, the blender must be mounted as free of vibration and as stable as possible. The earth (PE) connection of the hopper loaders must be made; conveying raw material generates static electricity.
Gravimix blenders are protected by two safety devices located on the front panel and the mixing chamber; when either is removed, power is cut and the blender stops. Warning labels are fitted on the motor(s), control box, user interface and front panel: danger of high voltage, beware of rotating parts and motor direction of rotation.