GB2076998A - Control of a butter conveying mechanism - Google Patents

Abstract

Butter from a container 1 is fed to a pump 5 by a screw conveyor 4 driven by a motor 3 whose speed is controlled in correspondence to the measured speed of the pump 5, while the speed of a motor 6 driving the pump 5 itself controlled in response to the amount of butter in a butter moulding machine 8, as determined by the position of a compressed air-operated piston 10. The position is measured by a potentiometer 11 driven by a rack 14. Limit switches 13, 14 switch off the pump 5 and the moulding machine 8 respectively when operated. The motor speeds are retroactively controlled using pulse type tachometers, the speed variations being effected by adding the correcting voltages to set values for the speed. <IMAGE>

Description

SPECIFICATION Apparatus for controlling the drive of a butter conveying mechanism The present invention relates to an apparatus for controlling the drive of a butter conveying mechanism for a butter moulding and packing machine, in which the butter is conveyed from a storage container or butter trolley by means of a motor-driven conveyor screw and is supplied to a speed-controllable butter pump with direct feeding into the compensating piston of the butter moulding machine.

As a result of the higher demands made on quality and the longer periods during which the product is kept any reinfection of the butter during transportation from the buttermaking machine or a storage container or the like to the packing machine must be avoided.

Thus, completely closed systems are desirable, which prevent any contact between the unpacked butter and the ambient air.

Therefore packing machine manufacturers have developed and put into use so-called compensating pistons which replace the hitherto conventional open butter vats of butter moulding and packing machines.

Such a compensating piston can take up a certain quantity of butter when the mould plate of the moulding machine performs a rotary movement. After the rotary movement a compressed air-operated piston compresses the butter into the moulds.

The compensating piston is filled by a butter pump to which the butter taken from the storage container is supplied by means of a motor-driven conveyor screw. The butter pump delivery is to be adapted to the actual take-off capacity of the packing machine in order to ensure a continuous filling of the compensating piston. However, minor fluctuations in the butter consistency can lead to considerable fluctuations in the supply capacity.

In order to eleminate this disadvantage it is known to use two-speed motors for driving butter pumps and their speed is controlled by two limit switches located on the compensating piston. However, this measure always leads to abrupt speed changes and consequently to weight fluctuations in the butter packs. In addition, a speed change brought about by a two-speed motor leads to additional energy being applied.

However, disturbance variables can even occur in butter trolleys or in storage containers when supplying the butter to the butter pumps. A too high screw conveyor speed can lead to changes in texture, which can in turn prejudice the quality, whilst air cavities can also form.

The problem of the invention is to provide fully automatic control for the drive of the butter conveying mechanism of a butter moulding and packing machine so as to avoid weight variations in the packed butter packs and prevent negative mechanical stresses on the butter texture butter being supplied in a continuously variable manner.

According to the present invention an apparatus is provided for controlling the drive of a butter conveying mechanism for a butter moulding and packing machine, in which the butter is conveyed from a storage container or butter trolley by means of a motor-driven conveyor screw and is supplied to a speedcontrollable butter pump with direct feeding into the compensating piston of the butter moulding machine, wherein is provided a control unit comprising at least tarn separate control loops, the first control fuzz being connected upstream of the drive motor of the butter pump and the second control loop being connected upstream of the drive motor of the conveyor screw, the conveyor screw drive being infinitely variable as a function of the momentary delivery of the butter pump and the latter as a function of the filling of the compensating piston and/or the output of the butter moulding and packing machine.

Further advantageous features and developments are set out in the subclaims.

The particular advantages resulting from the invention are that through a uniform supply of butter to the moulding and packing machine very accurate weight of the packed butter packs is ensured, together with limited mechanical stressing of the butter texture. The apparatus according to the invention also ensures a high degree of automation. A further advantage occurs in conveying the butter through the pipelines. As a result of a uniform conveying speed the silicate film used in the chemical cleaning of the pipeline system on the inner walls thereof is not damaged, so that there is no butter adhesion.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show: Figure 1 a butter pump control in a diagrammatic view.

Figure 2 a basic circuit diagram of the drive control.

In connection with the butter pump and conveying controls shown in Fig. 1 1 is a butter trolley containing the stored butter in the form of a butter roll 2. The butter is conveyed from butter roll 2 by means of a conveyor screw 4 driven by an electronically infinitely variable drive motor 3 to a butter pump 5. Butter pump 5 is constructed as a rotary pump with an also infinitely variable drive motor 6. There can be two or more butter pumps 5 instead of the one butter pump shown.

A pipeline 2 leads from butter pump 5 to a partly shown butter moulding and packing machine 8, having a compensating piston 9 for receiving the butter supplied by pipeline 7.

Compensating piston 9 can cqntain a certain quantity of butter if the not shown mould plate of the butter moulding and packing machine 8 performs a rotary movement. A compressed air-operated piston 10, subsequent to the rotary movement of the mould plate, compresses the butter in preciseiy metered form to give moulded pats which are subsequently packed.

A variable resistor in the form of a rotary potentiometer 11 is provided for monitoring the fill level of compensating piston 9. It is controlled by the fill level of compensating piston 9 by means of a rack 1 2 connected to piston 10 and supplies corresponding correction values to the drive control to be described hereinafter. A limit switch 1 3 or 1 4 is associated respectively with the upper and lower stroke positions of piston 10, upper limit switch 1 3 switching off butter pump 5 and lower limit switch 14 the butter moulding and packing machine 8.Between the two end positions of piston 10 of compensating piston 9 the optimum control of butter pump 5 is assumed by rotary potentiometer 11 (correction potentiometer) which, from the median position, is adjusted in the positive (+) direc- tion or negative (-) direction by means of rack 12.

A control unit 15, comprising two separate control loops 16, 1 7 is provided for the fully automatic drive control of the aforementioned apparatus. Control loop 1 6 is connected upstream of drive motor 6 of butter pump 5 and control loop 1 7 is connected upstream of the conveyor screw drive (drive motor 3). Control takes place by means a continuous true value/desired value comparison of the variables influencing the drive, taking account of the correction value K predetermined by rotary potentiometer 11 through the position of compensating piston 9.The conveyor screw drive can be continuously regulated as a function of the momentary delivery of butter pump 5 and the latter as a function of the momentary filling of compensating piston 9 and/or the packing capacity of the butter moulding and packing machine 8.

The operation of the control is described hereinafter by means of Fig. 2 in conjunction with Fig. 1, the same means being given the same reference numerals.

By means of a desired value adjuster 1 8 of control loop 1 6 the speed of drive motor 6 of butter pump 5 is preselected and by means of a line 1 9 the desired value Sp is superimposed on drive motor 6. A control drive 20 of control loop 16 associated with drive motor 6 returns electrical impulses via a line 22 to the electronics by means of an impulse generator 21 (actual value generator). The impulses correspond to the actual speeds drive motor 6 of butter pump 5 or to the actual value Ip.

This actual value Ip is now electronically compared with the desired value Sp. If necessary the speed of control drive 20 of drive motor 6 is automatically continuously varied or matched to the desired value Sp, independently of the comparison result, so that a constant predetermined speed and/or output of butter pump 5 is obtained.

According to the setting on the desired value adjuster 18, compensating piston 9 is filled from butter pump 5 via pipeline 7. As a function of the capacity of the butter moulding and packing machine 8 a certain quantity of butter is always located in the compensating piston 9. If the packing capacity is reduced, the degree of filling of compensating piston 9 rises. The rotary potentiometer 11 now has a negative influence on desired value Sp, so that automatically the speed of butter pump 5 is reduced. On increasing the packing capacity there is a positive change to the desired value Sp and the pump delivery rises correspondingly. Taking account of the correction value K the total desired value Sp to ic now set.

Following a stoppage to the butter moulding and packing machine 8 as a result of a paper change or the like, piston 10 is in the upper position and butter pump 5 is switched off by means of limit switch 1 3. After putting the butter moulding and packing machine 8 into operation limit switch 1 3 for stopping the butter pump 5 is released and pump 5 starts with a reduced speed. This speed corresponds to a low total desired value Sp to, i.e. the desired value Sp of desired value adjuster 1 8 minus the negative correction value K of rotary potentiometer 11 calculated-from the mean position of potentiometer 11.After a certain time the speed of drive motor 6 of butter pump 5 is automatically matched to the packing capacity of the butter moulding and packing machine. If the packing machine is also equipped with an automatic weight control, resulting corrections in packing output are immediately performed. As the packing machines only pack on a volume basis, the weight variations, e.g. due to different air contents and cavities,constitute disturbance variable requiring a readjustment is performed automatically with the aid of the aforementioned rotary potentiometer 11.

However, further disturbance variables can occur in butter trolley 1 on conveying the butter to butter pump 5. For example too high speeds of the conveyor screw 4 lead to changes in texture of the butter and consequently to a reduced quality. This also leads to the problem of air cavities.

Due to the aforementioned factors the appa- ratus according to the invention regulates the screw speed of the conveyor screw 4 as a function of the momentary delivery of butter pump 5. Electronically infinitely variable drive motor 3 of screw 4 is set to a primary speed by means of a desired value adjuster 23 of control loop 1 7 and by means of a line 24 this speed is superimposed in drive motor 3 in the form of a desired value ST. A control drive 25 of control loop 1 7 associated with drive motor 3 returns electrical impulses via a line 27 to the electronics by means of an impulse generator 26 (actual value generator), whose operation corresponds e.g. to impulse generator 21 of control drive 20.These impulses correspond to the actual speed of drive motor 3, i.e. an actual value 1T The actual speed, the actual value Ip of drive motor 6 of butter pump 5 is now superimposed on the desired value ST of the primary speed of drive motor 3 of conveyor screw 4, as is shown by line 28 in Fig. 1.

This leads to a screw speed increase with the total desired value ST to. In the case of a plurality of electronically driven butter pumps 5 with corresponding associated control loops 1 6 and drive motors 6, the control takes place in exactly the same way. As the desired value ST or ST to for the speed determination of conveyor screw 4 is limited as regards its magnitude, the actual values Ip are totalled when using several butter pumps 5, proportionally reduced and then superimposed on the desired value ST of screw 4 (connections a, b, c, in Fig. 2). The consequence of a stoppage of a butter pump 5 is a reduction in the speed of the conveyor screw drive.

Hereinafter the variables influencing the drive control and their reciprocal functional relationship are again described: Desired value pump (sup) + Correction value (K) - Desired value pump total (Spto) Actual value pump (Ip) + Desired value addition conveyor = Desired value cunueyurucrew total (ST to) An optical control of the controlled variables, particularly the actual values Ip and IT can take place by means of additional measuring lines 29, 30 (Fig. 2) connected with corresponding indicators 31, 32 in control unit 15.

In connection with the aforementioned drive control shown in detail in Fig. 2, reference numerals 33 to 36 designate variable-gain amplifiers, electronic control means, universal amplifiers and/or thyristor output stages of conventional design, combined with balancing resistors. Circuit variants other than that shown are conceivable and possible.

Claims (10)

1. An apparatus for controlling the drive of a butter conveying mechanism for a butter moulding and packing machine, in which the butter is conveyed from a storage container or butter trolley by means of a motor-driven conveyor screw and is supplied to a speedcontrollable butter pump with direct feeding into the compensating piston of the butter moulding machine, wherein is provided a con troi unit comprising at least two separate control loops, the first control loop being connected upstream of the drive motor of the butter pump and the second control loop being connected upstream of the drive motor of the conveyor screw, the conveyor screw drive being infinitely variable as a function of the momentary delivery of the butter pump and the latter as a function of the filling of the compensating piston and/or the output of the butter moulding and packing machine.

2. An apparatus according to claim 1, wherein a desired value adjuster and an actual value generator (impulse generator) are in each case provided for the variables influencing the drive and the actual value of the speed of the drive motor for the butter pump is superimposed on the predetermined desired value for the speed of the conveyor screw drive and the lift position of the compensating piston is superimposed as a correction value on the speed desired value of the drive motor of the butter pump.

3. An apparatus according to claims 1 and 2 with a plurality of electromotively driven butter pumps, wherein a control loop is connected upstream of each drive motor of a butter pump and the actual values of the butter pump speeds are totalled and proportionally reduced and are superimposed on the predetermined desired value of the speed of the conveyor screw drive.

4. An apparatus according to one or more of the claims 1 to 3, wherein for producing the correction value dependent on the filling level or the piston travel of the compensating piston a rotary potentiometer controlled by the piston travel is provided on the compensating piston which supplies the control loop for the butter pump drive a negative correction value reducing the output of the butter pump when the pistion rises above the median position and a positive correction value raising the delivery of the butter pump when the piston falls below the median position.

5. An apparatus according to claim 4, wherein the rotary potentiometer is controlled by a rack moved by the piston.

6. An apparatus according to one or more of the claims 1 to 5, where-in a limit switch is associated with each of the upper and lower travel end positions of the compensating piston, whereof the upper limit switch switches off the drive motor for the butter pump and the lower limit switch switches off the butter moulding and packing machine and wherein operationally the rotary potentiometer is arranged between the two limit switches.

7. An apparatus according to one or more of the claims 1 to 6, wherein the drive motors for the conveyor screw and the butter pump are controlled in continuous speed-regulatable manner by means of associated electronic control drives.

8. An apparatus according to one or more of,the claims 1 to 7, wherein a weight control device is associated with the butter moulding and packing machine.

9. An apparatus according to one or more of the claims 1 to 8, wherein the control loops have indicators for the optical representation of the control variables.

10. An apparatus for controlling the drive of a butter conveying mechanism for a butter moulding and packing machine substantially as described herein with reference to and as shown in the accompanying drawings.

LIST OF REFERENCE NUMERALS 1 Butter trolley 2 Butter roll 3 Drive motor 4 Conveyor screw 5 Butter pump 6 Drive motor 7 Pipeline 8 Butter moulding and packing machine 9 Compensating piston 10 Piston 11 Rotary potentiometer 12 Rack 1 3 Limit switch 14 Limit switch 1 5 Control unit 1 6 Control loop (Butter pump) 1 7 Control loop (Conveyor screw) 18 Desired value adjuster (control loop 16) 1 9 Line (Sp, Sp to) 20 Control drive (Butter pump) 21 Impulse generator 22 Line (Actual value Ip) 23 Desired value adjuster (control loop 17) 24 Line (ST, Sr to) 25 Control drive (conveyor screw) 26 Impulse generator 27 Line (Ir) 28 Line (Ip) 29 Measuring line 30 Measuring line 31 Indicators 32 Indicators 33 Variable gain amplifier 34 Control set 35 Universal amplifier 36 Thyristor output stages a, b, c Connections K Correction value