BE USED IN RELATION WITH A COMBINATION WEIGHER

FIELD OF THE INVENTION

The present invention relates to method and a system of operating a helical screw adapted to be used in relation with a combination weigher, to a control unit for a combination weigher, and a combination weigher with such a control unit.

BACKGROUND OF THE INVENTION

Batches such as a bag of food items having a pre-defined target weight are often made using combination weighers (sometimes referred to as multihead-weighers). Such a combination weigher commonly comprises a conical shaped distribution unit and elongated trenches that extend radially away from the periphery of the conical shaped distribution unit.

The conical shaped distribution unit is configured to receive food objects from an infeed unit such as an infeed conveyor placed above the conical shaped distribution unit and distribute the food items into the elongated trenches.

Each trench has an associated helical screw driven by a motor that via a rotation movement advances the received food items from an infeed end of the trenches to a releasing end of the trenches, where the food objects may be released into a weighing hopper, where one or more food items are weighed and temporarily stored.

Having as an example 12 such trenches, those who have a combined weight which fits into the target weight being generated are released simultaneously to a common receiving area, where the food objects may e.g. be placed into a bag.

Existing combination weighers may be configured to change the rotational speed (RPM) of the motor. The control unit may e.g. be operable to control RPM and/or operational duration of the motor to prepare well-defined portions of food items in the weighing hopper. The change in RPM may e.g. be carried with the intention to optimize dosing, and it could depend on a signal that is fed to the control unit e.g. from a weighing hopper etc. In accordance therewith, the control unit may adjust the period of time and/or the motor speed in order to adjust the dosage of product material from each weighing hopper. A common problem today is that the food products may get caught between the screw and the trench which cause the helical screws to stall and therefore temporal deactivation of the weighing hopper associated to this particular trench. This means that instead of having 12 weighing hoppers active, there are only 11. This has a significant effect on the yield since the optimal weight combination for reaching the weight target requires many active trenches. Obviously, this will be more severe when 3 or 4 screws are blocked. This can result in late detection by an operator, which in the end manually removes the food object therefrom meaning that several minutes or more can pass until stalling is detected and solved.

Also, this can cause a risk for the operator if the helical screw suddenly starts to run again. Also, the time delay until this is detected means that the combination weigher is running with e.g. only 8-11 trenches (referring to the example above) which reduces the throughput and the yield of the batching process.

SUMMARY OF THE INVENTION

On the above background it is an object of embodiments of the present invention to provide an improved method, a system, and control unit for operating such combination weighers, and a combination weigher with such a control unit with the aim of reducing or even eliminating stalling helical screws.

In a first aspect of the invention, a method is provided for operating helical screws adapted to be used in relation with a combination weigher, where the combination weigher comprises a plurality of elongated trenches, where within each of the elongated trenches such a helical screw is provided and driven by a motor such as a stepper motor, where the helical screw is configured to advance, via an initial revolutions per minute (RPM) value and an initial torque value of the helical screw, received food items from receiving ends of the trenches towards releasing ends of the trenches where the food items are released therefrom, the method comprising: a) identifying if a change in the RPM value or a change in the torque value has occurred from the initial RPM value or the initial torque value of the helical screw, and, in case a change is identified, b) automatically adjusting the helical screw to another RPM value different from the initial RPM value or to another torque value different from the initial torque value. Accordingly, five series of embodiments are disclosed and covered by the broadest definition of the invention:

1) In a first series of embodiments, if a change in the RPM value is identified, the helical screw is automatically adjusted to another RPM value different from the initial RPM value.

2) In a second series of embodiments, if a change in the torque value is identified, the helical screw is automatically adjusted to another torque value different from the initial torque value. 3. In a third series of embodiments, if a change in the torque value is identified, the helical screw is automatically adjusted to another RPM value different from the initial RPM value, and

4) In a fourth series of embodiments, if a change in the RPM value is identified, the helical screw is automatically adjusted to another torque value different from the initial torque value.

5) In a fifth series of embodiments, if changes both in the RPM value and torque value are identified, the helical screw is automatically adjusted to another RPM value and torque value different from the initial RPM value and initial torque value.

The combination weigher may as an example be a linear combination weigher, or “circular” combination weigher comprising e.g. a conical shaped distribution unit and multiple of such elongated trenches that extend radially away from the periphery of the conical shaped distribution unit. During operation, in case of such a circular combination weigher, the conical shaped distribution unit receives food objects from an infeed unit such as an infeed conveyor placed above the conical shaped distribution unit and distributes the received food items into the elongated trenches. At the end and below the trenches, there are weighing hoppers configured to receive food items released from the releasing ends of the trenches. When generating batches of pre-fixed weight, e.g. 3 kg poultry fillet, the optimal combination of weighing hoppers is selected given the minimal giveaway, i.e. as close as possible to the 3 kg (typically slightly above), and these selected weighing hoppers are then released simultaneously into a common receiving area, e.g. a bag area, where the batch is accumulated. To keep the optimal performance, highest throughput, and maximal yield (minimal overweight) it is of outmost importance that preferably all trenches/helical screws with the associated combination weighers are active. The initial RPM or torque value could be considered as a so called set-value, i.e. an RPM value or torque value which is desired.

While existing combination weighers may change RPM to adjust the dosage of product material from each weighing hopper, e.g. based on a weight signal, the present invention provides a change when detecting a deviation between the actually obtained RPM or torque and the initial value of the RPM or torque.

Accordingly, the set-value is replaced by a different value, when the motor is unable to obtain the desired speed or torque.

This is different from a traditional system which would try to re-gain the original setvalue or which may change the set-value e.g. based on a signal from a weighing hopper in order to optimize dosing etc.

The identification of a change in RPM or torque may e.g. be the identification that the helical screw does not rotate at all, or that there is no torque at all.

In case the RPM value is lower than the initial RPM value, the RPM value may be adjusted to a lower RPM value with increased torque. Accordingly, by reducing the RPM, the torque from the helical screw is increased and therefore the possibility of unloosing the blocking is increased significantly and thus the possibility of unloosen the blocking of the helical screw. This not only reduces, or even eliminates, the instances where a complete blocking occurs, but also improves the yield because of the larger number of weighing hoppers being active. Also, the throughput of the process of making batches of pre-fixed target weight is improved because of less waiting time to find the most optimal weighing combination to reach the weight target. More importantly, less manual intervening is needed to unloosen the blocking meaning that the safety increases.

In case the RPM value is higher than the initial RPM value, the RPM value may be adjusted to a higher RPM value. This is of particular advantage e.g. as a subsequent step after e.g. unloosen the blocking of the helical screw where less torque is needed and the throughput of process is to be increased by increasing the amount of advancing speed of the received food items from receiving ends of the trenches towards releasing ends of the trenches.

In one embodiment, said steps a) and b) are repeated until the change in the RPM value is within a pre-defined threshold limit from the previous RPM value. Accordingly, multiple different RPM value steps may be possible, like an automatic gear shift, where e.g. for a first RPM value, the first torque value is T1, if a stalling is detected, the RPM value 1 is reduced to a RPM value 2 where the torque is increased to T2 > T1. If the new RPM value is yet not within a threshold limit of the previous RPM value 2, the RPM value may be reduced further to RPM value 3 with where the torque is increased further to T3>T2 > T1. If at this moment, the RPM value is within a threshold limit for RPM value 3, it is an indication that the reason for the stalling has been removed. A subsequent step might then be to increase the RPM value, e.g. to the initial RPM value 1.

In an embodiment, if the change in the RPM value is not within pre-defined threshold limit from the previous RPM value, the helical screw is stopped. If the RPM value in the above mentioned examples, is within a threshold limit for RPM value 3, then the helical screw may be stopped.

It should be noted that this may also apply if, for a first RPM value where the first torque value is T 1 and a stalling is detected, the RPM value 1 is reduced to an RPM value 2 where the torque is increased to T2, and if still the new RPM value is yet not within a threshold limit of the previous RPM value 2 then the helical screw is stopped.

The motor may be any type of a motor know to a person skilled in the art, such as, but not limited to, a stepper motor or a brushless DC motor.

In one embodiment, the motor comprises a tacho sensor to monitor the angular position of the motor, where the input from the tacho sensor indicating the angular position of the motor is used in identifying if a change in the RPM value has occurred. As an example, in case the motor is a stepper motor, one round may be set for 200 steps (it may of course be less than 200 steps or larger than 200 steps). Also, the motor may be defined to have 4 tacho pulses (may of course be different from 4, e.g. less or higher than four) for one round so that one tacho pulse is 50 steps. In this case, detecting stalling may be based on defining a maximum number of steps acceptable between tacho pulses. An example of such a maximum number of steps setting is 75 steps, meaning that the motor can move the regular 50 steps, and lose additional up to 25 steps before registering a stall. Accordingly, said step of identifying if a change in the RPM value has occurred is where no tacho pulse is detected.

In one exemplary embodiment, the motor can be any type of electrical driven motor and where the step of identifying if a change in the RPM value has occurred from the initial RPM value of the helical screw comprises measuring power consumption related value of the power source powering the helical screw at the initial RPM value and comparing the power consumption related value with a pre-defined target value associated to the initial RPM value. If the measured power consumption related value is different from the pre-defined target value, then initial RPM value is automatically adjusted to said another RPM value that is different from the initial RPM value.

According to a second aspect, a system is provided for operating helical screws adapted to be used in relation with a combination weigher, where the combination weigher comprises a plurality of elongated trenches, where within each of the elongated trenches such a helical screw is provided and driven by a motor such as a stepper motor, where the helical screw is configured to advance, via an initial revolutions per minute (RPM) value and an initial torque value of the helical screw, received food items from receiving ends of the trenches towards releasing ends of the trenches where the food items are released therefrom, the system comprising: a) a detection device for identifying if a change in the RPM value or torgue value has occurred from the initial RPM value or initial torque value of the helical screw, where in case a change is identified, b) a control unit connected to the detection device configured to operate the motor of the helical screw on the basis on the identified change in the RPM value or torque value so that if a change is identified to automatically adjust the initial RPM value or torque value to another RPM value or torque value different from the initial RPM value or torque value.

In an embodiment, the motor is an electrical driven motor and where the step detection device is configured measure power consumption related value of the motor at the initial RPM value and comparing the power consumption related value with a pre-defined target value associated to the initial RPM value.

In another embodiment, the motor comprises a tacho sensor to monitor angular position of the motor, where the input from the tacho sensor indicating the angular position of the motor is used as an input in identifying if a change in the RPM value has occurred.

According to a third aspect a control unit is provided for controlling revolutions per minute (RPM) or torque of a motor which rotates a helical screw in a combination weigher. The control unit is configured to define a set-value of the RPM or torque.

The control unit may e.g. be implemented as software in a computer system, and the set-value is e.g. defined in a flash memory of the control unit. The control unit is further configured for detecting a deviation between the obtained motor speed or torque and the defined set-value, and if the deviation exceeds a threshold, to change the defined set-value of the RPM or torque.

Five series of embodiments are disclosed:

1) In a first series of embodiments, the control unit is configured to define a set-value of the RPM, and for detecting a deviation between the obtained RPM and the defined setvalue, and if the deviation exceeds a threshold, to change the defined set-value.

2) In a second series of embodiments, the control unit is configured to define a setvalue of the torque, and for detecting a deviation between the obtained torque and the defined set-value, and if the deviation exceeds a threshold, to change the defined set-value.

3) In a third series of embodiments, the control unit is configured to define a set-value of the torque, and for detecting a deviation between the obtained torque and the defined setvalue, and if the deviation exceeds a threshold, to change a set-value defined for the RPM.

4) In a fourth series of embodiments, the control unit is configured to define a setvalue of the RPM, and for detecting a deviation between the obtained RPM and the defined set-value, and if the deviation exceeds a threshold, to change a set-value defined for the torque.

5) In a fifth series of embodiments, the control unit is configured to define a set-value both for the RPM and torque, for detecting a deviation between the obtained RPM and the defined set-value related to the RPM, for detecting a deviation between the obtained torque and the defined set-value related to the torque, and if a deviation exceeds a threshold, to change a set-value defined for the torque or RPM.

Optionally, the control unit may be configured to adjust a motor control variable for obtaining a motor speed or torque corresponding to the defined set-value. The adjustment may be carried out in accordance with known control principles, and it may involve e.g. a P, PI, PID, or PD control in a closed loop. The control unit would strive to obtain and maintain rotation at the RPM or torque corresponding to the set-value by adjusting available parameters, e.g. related to frequency, voltage, and/or current of the electrical power signal driving the motor. The desired RPM or torque, i.e. the set-value, may normally be obtained when there is no excessive loading, e.g. when the helical screw is able to convey food items freely.

In case of excessive loading, e.g. when food items stick in the conveyor, the control unit may experience a deviation between the obtained RPM or torque and the set-value e.g. if it is unable to obtain the desired speed or torque within the limits of the available control variables.

If the deviation between the desired set-value and the obtained RPM or torque exceeds a threshold, e.g. a fixedly or variably defined threshold, the control unit changes the defined set-value and will therefore no longer try to obtain the previously defined set-value. Instead, the control unit will now adjust the available control parameters in an attempt to reach the new set-value.

The control unit may be configured with at least two predefined set-values and to switch between the at least two predefined set-values upon detecting a deviation between the obtained RPM or torque and the defined set-value. As an example, the motor may switch from a set-value of 20 RPM to a set-value of 10 RPM if the deviation between the obtained RPM and the set-value exceeds a threshold. One of the at least two predefined set-values could be zero RPM, corresponding to stopping the motor if the deviation between the obtained RPM and the set-value exceeds a threshold.

The control unit may be configured to reduce the defined set-value of the RPM if the obtained motor speed is lower than the defined set-value of the RPM, and the control unit may be configured to increase the defined set-value of the RPM if the obtained motor speed is higher than the defined set-value of the RPM.

The steps of detecting a deviation between the obtained motor speed and the defined set-value, and the step of changing the defined set-value of the RPM may be repeated until a difference between the obtained motor speed and the defined set-value is within a threshold.

According to a fourth aspect a combination weigher is provided. The combination weigher comprises a plurality of elongated trenches, a helical screw in each trench, and a motor for each screw, the motor being arranged to drive the screw and thereby convey items in the trench, the combination weigher further comprising a control unit arranged to control revolutions per minute (RPM) of each motor and configured to define a set-value of the RPM and to adjust a motor control variable for obtaining a motor speed corresponding to the defined set-value of the RPM, wherein the control unit is further configured for detecting a deviation between the obtained motor speed and the defined set-value, and if the deviation exceeds a third threshold, to change the defined set-value of the RPM.

In general, the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

LIST OF NUMBERED FURTHER EMBODIMENTS

1. A method of operating helical screws adapted to be used in relation with a combination weigher, where the combination weigher comprises a plurality of elongated trenches, where within each of the elongated trenches such a helical screw is provided and driven by a motor, where the helical screw is configured to advance, via an initial revolutions per minute (RPM) value of the helical screw, received food items from receiving ends of the trenches towards releasing ends of the trenches where the food items are released therefrom, the method comprising: a) identifying if a change in the RPM value has occurred from the initial RPM value of the helical screw, where in case a change is identified, b) automatically adjusting the helical screw to another RPM value different from the initial RPM value and initial torque value.

2. The method according to embodiment 1, wherein in case the RPM value is lower than the initial RPM value, the RPM value is adjusted to a lower RPM value with increased torque.

3. The method according to embodiment 1, wherein in case the RPM value is higher than the initial RPM value, the RPM value is adjusted to a higher RPM value with decreased torque. 4. The method according to any of the preceding embodiments, wherein steps a) and b) are repeated until the change in the RPM value is within a pre-defined first threshold limit from the previous RPM value.

5. The method according to any of the preceding embodiments, wherein in case the change in the RPM value is not within a pre-defined second threshold limit from the previous RPM value the helical screw is stopped.

6. A system for operating helical screws adapted to be used in relation with a combination weigher, where the combination weigher comprises a plurality of elongated trenches, where within each of the elongated trenches such a helical screw is provided and driven by a motor such as a stepper motor, where the helical screw is configured to advance, via an initial revolutions per minute (RPM) value of the helical screw, received food items from receiving ends of the trenches towards releasing ends of the trenches where the food items are released therefrom, the system comprising: a) a detection device for identifying if a change in the RPM value has occurred from the initial RPM value of the helical screw, where in case a change is identified, b) a control unit connected to the detection device configured to operate the motor of the helical screw on the basis on the identified change in the RPM value so that if a change is identified to automatically djust the initial RPM value to another RPM value different from the initial RPM value.

7. The system according to embodiment 6, wherein the motor is an electrical driven motor and where the step detection device is configured measure power consumption related value of the motor at the initial RPM value and comparing the power consumption related value with a pre-defined target value associated to the initial RPM value.

8. The system according to embodiment 6, wherein the motor comprises a tacho sensor to monitor angular position of the motor, where the input from the tacho sensor indicating the angular position of the motor is used as an input in identifying if a change in the RPM value has occurred. 9. The system according to any of the embodiments 6 to 8, wherein the motor is selected from a stepper motor or a brushless DC motor.

10. A control unit arranged to control revolutions per minute (RPM) of an associated motor which rotates a helical screw in a combination weigher, the control unit being configured to define a set-value of the RPM and to drive the motor at an RPM corresponding to the defined set-value, wherein the control unit is further configured for detecting a deviation between the obtained RPM and the defined set-value, and if the deviation exceeds a third threshold, the control unit is configured to change the defined set-value and to drive the motor corresponding to the changed set-value.

11. The control unit according to embodiment 10, configured to adjust a motor control variable for obtaining an RPM of the associated motor corresponding to the defined set-value.

12. The control unit according to embodiment 10 or 11, configured with at least two predefined set-values and to switch between the two predefined set-values upon detecting a deviation between the obtained RPM and the defined set-value.

13. The control unit according to any of embodiments 10-12, wherein the control unit is configured to reduce the defined set-value if the obtained RPM is lower than the defined setvalue.

14 The control unit according to any of embodiments 10-12, wherein the control unit is configured to increase the defined set-value if the obtained RPM is higher than the defined set- value.

15. The control unit according to any of embodiments 10-14, wherein the steps of detecting a deviation between the obtained RPM or torque and the defined set-value, and the step of changing the defined set-value is repeated until a difference between the obtained RPM and the defined set-value is within a fourth threshold. 16. The control unit according to any of embodiments 10-15, configured for determining the deviation between the obtained RPM or torque and the defined set-value by measuring a power consumption of the motor and comparing the power consumption with a reference power consumption stored in the control unit and related to consumption when the RPM corresponds to the defined set-value.

17. A combination weigher comprising a plurality of elongated trenches, a helical screw in each trench, and a motor for each screw, the motor being arranged to drive the screw and thereby convey items in the trench, the combination weigher further comprising a control unit arranged to control revolutions per minute (RPM) of each motor and configured to define a set-value of the RPM and to adjust a motor control variable for obtaining an RPM corresponding to the defined set-value, wherein the control unit is further configured for detecting a deviation between the obtained RPM and the defined set-value, and if the deviation exceeds a fifth threshold, to change the defined set-value.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

Figure 1 shows an embodiment of a flow chart of a method according to the present invention of operating helical screws adapted to be used in relation with a combination weigher,

Figure 2 shows an example of a helical screw,

Figure 3 shows a block diagram of an embodiment of the method according to the present invention for operating a helical screw driven by a motor and adapted to be used in relation with a combination weigher, and

Figure 4 shows one example of measuring change in RPM.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a method of operating helical screws adapted to be used in relation with a combination weigher. Figure 1 depicts an example of such a combination weigher 100 comprising a conical shaped distribution unit 101, multiple of elongated trenches 102 that extend radially away from the periphery of the conical shaped distribution unit 101 with a helical screw 104 placed therein and operated by a motor and a control unit.

During operation, the conical shaped distribution unit 100 receives food objects from an infeed unit (not shown) such as an infeed conveyor placed above the conical shaped distribution unit and distributes the received food items into the elongated trenches. At the end and below the trenches, there are weighing hoppers 103 configured to receive food items released from the releasing ends of the trenches. When generating batches of pre-fixed weight of batches, the optimal combination of weighing hoppers is selected given the minimal giveaway from the target weight and these selected weighing hoppers are then released simultaneously into a common receiving area (not shown), e.g. a bag area.

Figure 2 shows an example of such a helical screw having helical portion 201 and a mounting end which is attached to a motor 203.

Figure 3 shows a block diagram of an embodiment of the method according to the present invention for operating a helical screw driven by a motor and adapted to be used in relation with a combination weigher, e.g. such as the one shown in figure 1, where the helical screw is configured to advance, via an initial revolutions per minute (RPM) value of the helical screw, received food items from receiving ends of the trenches towards releasing ends of the trenches where the food items are released therefrom.

In a first step 301, an initial Rounds Per Minute (RPM) value of the helical screw is set, e.g. to 666 HZ.

In a second step 302, it is determined if a change in the RPM value has occurred from the initial RPM 666HZ value of the helical screw. As an example, if the motor is an electrical driven motor this may be done by measure power consumption related value of the motor at the initial RPM 666HZ value and comparing the power consumption related value with a predefined target value associated to the initial RPM value, e.g. by measuring the current in the motor. A deviation of e.g. 5% from this initial value may be acceptable but more than 5% deviation may trigger that a change in the RPM value from the initial value has taken place. Another example of measuring this is depicted in figure 4, namely, to provide the motor which may be a stepper motor with a tacho sensor to monitor angular position of the motor, where the input from the tacho sensor indicating the angular position of the motor is used as an input in identifying if a change in the RPM value has occurred. As shown here, one round may be set for 200 steps. Also, the motor may be defined to have 4 tacho pulses for one round so that one tacho pulse is 50 steps. In this case, detecting stalling may be based on defining a maximum number of steps acceptable between tacho pulses. An example of such a maximum number of steps setting is 75 steps, meaning that the motor can move the regular 50 steps, and lose additional up to 25 steps before registering a stall. Accordingly, said step of identifying if a change in the RPM value has occurred is where no tacho pulse is detected.

If no change is detected, the motor runs at the same initial RPM value.

In a third step 303, if a change in the RPM value is detected but it is within an acceptable limit, then yet the initial RPM value is kept.

In a fourth step 304, if the change of the RPM value exceeds a pre-defined threshold value (e.g. outside said 5%), the RPM value is automatically decreased to a lower RPM value 304, e.g. 333HZ, where for this particular motor which may be a stepper motor has a characteristics where the decrease in the lower RPM value results in an increase in the torque.

In a fifth step 305, if a change in the RPM value is within a pre-define threshold from this new 333Hz value, that indicates that the stalling has been solved and the RPM value is set back to the initial 666Hz value.

In a sixth step 306, if the change of the RPM is not within a pre-defined threshold limit for the 333Hz value, then the stalling is still present, and the motor is stopped 307.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.