AU628307B2

AU628307B2 - Crusher controller

Info

Publication number: AU628307B2
Application number: AU26853/88A
Authority: AU
Inventors: Geoffrey Lynn Cragg; Johannes Hermanus Potgieter
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1987-12-15
Filing date: 1988-12-14
Publication date: 1992-09-17
Anticipated expiration: 2008-12-14
Also published as: GB2211004B; AU2685388A; GB2211004A; GB8829243D0

Description

COMMONWEALTH OF AUSTRALIA PATENTS ACE 1952 NAME ADDRESS OF APPLICANT: De Beers Industrial Diamond Division (Proprietary)Limited Main Street Johannesburg Transvaal Republic of South Africa NAME(S) OF IN4VENTOR(S): Gfeoffrey Lynn CRAGO Johannes Hermanus POTGIETER ADDRESS FOR SERVICE: DAVIES COWLSON Patent Attorneys so Little Collins Street, Melbourne, 3000.

0 00 COMPLETE SPEiCIFICATION FOR THE INVENTION ENTITLED: 00:* Crusher cop~troiler The foli',wicg statement is a full description of this invention, including the best method of pez-for-ning it known to me/us:- -2 I i 'r -2 BACKGROUND OF THE INVENTION This invention relates to a controller for a motordciven ondo cC .ne-vo ov<? 'awc c driven cone-type crusher.

Cone-type crushers are known in which a generally frusto-conical crusher head rotates eccentrically in a crusher gap defined between edges of the bowl and the crusher head. The space between the crusher head and the sides of the bowl is annular in section, and decreases to a minimum at the actual crusher gap. In one example of such a crusher, the crusher head is rotated by an electric motor, and a hydraulic system controls the vertical position of the crusher head, and thus the spacing between the crusher head and the bowl.

The gap or close side setting (CSS) of the crusher, which is the minimum spacing between the crusher head and the bowl, affects the throughput of the crusher, as well as the power drawn by the crusher motor, the *o pressure in the hydraulic system controlling the CSS, Sand the size distribution of the crushed material discharged from the crusher. In certain applications, particularly in the recovery of diamonds, an optimum CSS exists for each crusher for a particular material. It is therefore desirable to o r* operate the crusher with a fixed CSS.

e I/u I1 3- A version of the crusher described above has an automatic control system which monitors the power drawn by the crusher motor and the pressure in the hydraulic system controlling the vertical position of the mainshaft and thus the CSS, and increases the CSS to reduce the load on the crusher if either of these variables exceeds a predetermined overload limit.

This means that if the crusher is operated close to its maximum capacity, relatively frequent overloads will occur in practice, causing the CSS to be increased and thus leading to non-optimal crushing.

The alternative is to limit the introduction of feed to the crusher, thus ensuring that the power and cone pressure remain below their predetermined overload limits. This reduces the overall throughput potential of the crusher.

In most cases, the situation is complicated by variations with time in the physical and mechanical i characteristics of the material passed through the crusher. As a result of these variations, a fixed .material throughput at different times can result in an overload condition involving either the power, the cone pressure ox the level of material in the crusher bowl. The variable most likely to exceed its overload limit at a given time can be referred to as the dominant variable.

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0* 0 J S-4 SUMMARY OF THE INVENTION According to the invention there is provided a method of controlling a motor-driven cone-type crusher in which a crusher gap setting between a crusher head and a crusher bowl is hydraulically controlled to prevent the motor power and pressure exerted on the crusher head from exceeding respective predetermined limits, the method including the steps of: monitoring a first variable related to the power drawn by the crusher motor; monitoring a second variable related to the pressure exerted on the crusher head; monitoring a third variable related to the level of material to be crushed in the bowl; selecting a variable to be controlled from the first, second and third variables; determining a desired setpoint of the controlled variable; controlling the rate of feed of material to the crusher to maintain the controlled variable at 0' or near the desired setpoint; 0 0

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pII and effectively lowering the desired setpoint of the controlled variable if either of the remaining variables exceed respective predetermined limits, in order to prevent an increase of the crusher gap above a chosen setting.

A dominant variable may be identified among the first, second and third variables. The controlled variable may be the dominant variable, or one of the other variables, Preferably, the dominant variable will also be the controlled variable.

Identification of the dominant variable and subsequent selection of the controlled variable may be performed manually, or automatically on the basis of historical data relating to the operation of the crusher.

The value of the desired setpoint may be selected manually, or automatically by an optimisation algorithm.

Further according to the invention there is provided a controller for a motor-driven cone-type crusher in which a crusher gap setting between a crusher head and a crusher bowl is hydraulically controlled to prevent the motor power and pressure exerted on the

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55* O0 S ooo S. S 0 O 0 L -6crusher head from exceeding respective predetermined overload limits, the controller comprising: first sensor means for monitoring a first variable related to the power drawn by the crusher motor; second sensor means for monitoring a second variable related to the pressure exerted on the crusher head; third sensor means for monitoring a third variable related to the level of material to be crushed in the bowl; means for selecting a variable to be controlled from the first, second and third variables; 00 of means for determining a desired setpoint of the controlled variable; feed rate control means for controlling the rate of feed of material to the crusher to maintain the controlled variable at or near the desired setpoint; Sand setpoint control means for effectively lowering the desired setpoint if either of the remaining variables exceed respective soot@: predetermined limits, in order to prevent an ***00

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S S -7increase of the crusher gap above a chosen setting.

The means for selecting the controlled variable may be adapted to identify a dominant variable from among the first, second and third variables, and to select either the dominant variable or one of the other variables as the controlled variable.

The means for selecting the controlled variable may be adapted to allow manual selection of the controlled variable.

Alternatively, the means for selecting the controlled variable may be adapted to perform the selection automatically, on the basis of historical data relating to the operation of the crusher.

The means for determining the desired setpoint may be adapted to allow manual selection of the value of the 20 desired setpoint, or to determine the value of the desired setpoint automatically by an optimisation algorithm.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention will now further be described by way of example only with reference to the accompanying drawings in which: 30 Figure 1 is a schematic illustration of a known cone-type crusher; and 910219,wpWdk,26853ct 1 7 -8 Figure 2 is a schematic block diagram of a controller according to the invention for use with the crusher of Figure 1.

DESCRIPTION OF AN EMBODIMENT Referring to Figure 1, a cone-type crusher comprises a bowl 10 which surrounds a frusto-conical crusher head 12. The bowl 10 defines a gap of annular section around the crusher head, which decreases towards the lower end of the crusher head. The effective crusher gap or close side setting (CSS) of the crusher is defined by the minimum width of a zone

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14 towards the lower edge of the crusher head. The crusher is arranged to allow material to be fed through an opening 16 into the bowl 10. An electric motor 18 eccentrically rotates the crusher head via a reduction drive 20, causing the material fed into the crusher to be crushed as it descends through the bowl towards the gap 14.

The crusher head 12 is mounted on a main shaft 22 which is held in a sleeve 24. The lower end of the shaft 22 slides in the sleeve 24 like a piston. A source 26 of hydraulic fluid is connected via a pump 28 and a hydraulic line 30 to the sleeve 24. A controller 32 has sensors 34 and 36 which monitor the power drawn by the motor 18 and the pressure in the hydraulic line 30, respectively. The amount of hydraulic fluid in the sleeve 24 is varied by the K I i go

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egos 5 *i 0 so s 9 pump 28 in order to maintain a preset crusher gap.

If either the motor power or the hydraulic pressure rise above a predetermined limit, the controller 32 automatically reduces the amount of hydraulic fluid in the sleeve 24, increasing the crusher gap setting or CSS, and thereby reducing the overload.

Referring now to Figure 2, the controller ofA the invention is illustrated schematically. The crusher system of Figure 1 is illustrated by a block 40 which should be understood to include the crusher, its motor system, its hydraulic adjustment system, and the conventional controller 32. The controller vEf tnts includes three sensors, which sense respectively the pressure in the hydraulic system of the crusher, the power drawn by the crusher motor, and the level of material in the crusher bowl. The first mentioned two sensors can be the sensors 34 and 36 described above. The outputs of the respective sensors are fed to a selection circuit 42 which allows any one of the three measured variables to be selected as a variable to be controlled. This selection may be manually performed or performed automatically in the selection circuit 42 on the basis of historical data. As it is preferable to maintain direct control over the variable most likely to enter an overload regime (a so-called dominant variable) the selection process should preferably involve identification of a dominant variable and its selection as the controlled variable. However, ,t should a non-dominant variable be selected as the controlled variable, this control method will nevertheless ensure that the control objectives are met.

The controlled variable is fed via a comparator 44, which compares the controlled variable with a setpoint, to a feed rate controller 46 in a conventional feedback control loop. The control algorithm used in the controller 46 may be, amongst others, a P, PI or PID algorithm. This loop functions to maintain the controlled variable close S" to the setpoint by adjusting the rate of ore feed to the crusher. Normally, the setpoint will be chosen so that the crusher operates close to its maximum capacity. According to which variable is selected as th controlled variable, appropriate tuning constants are fed from the selection circuit 42 to the controller 46, to adjust the characteristics of the feedback loop appropriately.

The two remaining variables, termed override variables 1 and 2, are fed to a setpoint control *I circuit which compares these variables with predetermined limits. A desired setpoint for the feedback loop is fed to the setpoint modification S* circuit by a desired setpoint selection circuit 68.

This selection circuit could involve generation of a fixed but operator-selectable desired setpoint or a desired setpoint updated periodicelly and r_ I 11automatically on the basis of historical data to suit changing conditions. The second variable is fed to each of two comparators 48 and 50, which compare the value of this variable with first and second preselected alarm levels. The comparator 48 compares the second variable with a "HI" limit, while the comparator 50 compares the second variable to a "HI HI" limit, both of which will fall below the predetermined overload limits set on the conventional controller. Similarly, comparators 52 and 54 compare the third variable to a "HI" limit and a "HI HI" limit.

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The outputs of the comparators 48 and 52 are fed to an OR gate the output of which controls a switching circuit 58. As illustrated in the drawing, and assuming that neither of the two remaining variables have exceeded the "HI" limit, the switching device 58 is configured as shown, and a signal corresponding to a desired setpoint of operation of the crusher is connected through the switching element to the rest of the circuit. If either of the remaining variables exceeds the respective "HI" limit, the upper switch of the switching element 58 is opened and the lower switch is closed, connecting a subtractor 60 to the rest of the circuit. The subtractor 60 is configured to reduce the desired setpoint value at a predetermined rate, until the value of the desired setpoint has been decreased by the full value of the setpoint decrease signal the first, second and third variables; determining a desired setpoint of the controlled variable; i o S- 12 applied to it. This function can be implemented by digital or analogue techniques.

In a similar configuration to that described above, the outputs of the comparators 50 and 54 are applied to an OR gate 62, which controls a second switching element 64. A second subtractor 66 decreases the value of the modified setpoint from the previous part of the circuit by a predetermined value, and at a predetermined rate, when either of the remaining variables exceeds a predetermined "HI HI" alarm level. The output of the switching element 64 is applied to the comparator 44 in the feedback control loop.

It will thus be apparent that where neither of the o. remaining variables exceeds the predetermined alarm levels, the setpoint which is applied to the cumparator 44 will be exactly the predetermined desired setpoint. If either of the variables exceed :i the predetermined "HI" limits, but not the predetermined "HI HI" limits, the setpoint value which is applied to the comparator 44 will effectively be ramped down to a certair Value at a controlled rate, lowering the feed rate to the crusher, and consequently decreasing all three variables. If either of the. ables nevertheless exceeds its respective "HI aI" limit, the set point will be further decreased. The effect ol the controller is thus to lower the setpoint whenever i feed rate control means for controlling the rate of feed of material to the crusher to maintain the controlled variable at or near the desired setpoint; /3 L I i i

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13 1 i either of the non-controlled (or override) variables increases to a point which indicates that overload of the crusher is imminent. By reducing the rate of feed before overload occurs, the conventional control circuit 32 can be prevented from coming into operation and increasing the CSS or crusher gap setting. This in turn improves the consistency of the crushed material.

Should the gap be increased despite the efforts of the controller of the invention to prevent the power or pressure exceeding the limits set in the .conventional controller, the desired setpoint is Sramped down continually until the conventional controller returns the gap to its predetermined optimal setting. Upon the gap being returned to its optimum, the setpoint is ramped up again to the value determined by the setpoint modification circuit in Figure 2.

It will be appreciated that the controller illustrated in Figure 2 is represented only schematically. In practice, circuitry will be incorporated to measure the respective variables over a period of time, so that the setpoint decreasing action will only be initiate, when these variables have exceeded their predeterminei limits for longer S..i than a certain period of time. Once the relevant variable has decreased below its alarm limit for a predetermined period of time, the modified set point 0 14 will be ramped up to its original value once again.

It will also be appreciated that the control strategy described may be implemented on a number of hardware con~figurations, and that it could be incorporated in the hardware of the conventional controller utilised to manipulate the crusher mainshaft position or as a separate entity.

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Claims

1. A method of controlling a motor-driven cone-type crusher in which a crusher gap setting between a crusher head and a crusher bowl is hydraulically controlled to prevent the motor power and pressure exerted on the crusher head from exceeding respective predetermined limits, the method including the steps of: monitoring a first variable related to the power drawn by the crusher motor; e monitoring a second variable related to the pressure exerted on the crusher head; monitoring a third variable related to the level of material to be crushed in the bowl; 00" selecting a variable to be controlled from the first, second and third variables; determining a desired setpoint of the controlled variable; controlling the rate of feed of material to the crusher to maintain the controlled variable at or near the desired setpoint; 0i S- 6 and effectively lowering the desired setpoint of the controlled variable if either of the remaining variables exceed respective predetermined limits, in order to prevent an increase of the crusher gap above a chosen setting.

2. A method according to claim 1 wherein a dominant variable is identified among the first, second and thir'd variables, the controlled variable corresponding to the dominant variable. S* Ce

3. A method according to claim 2 wherein the dominant variable is identified automatically on the basis of historical data relating to the operation of the crusher.

4. A method according to claim 1 wherein the controlled variable is selected manually.

5. A method according to any one of claims 1 to 4 wherein the value of the desired setpoint is 0* selected manually.

6. A method according to any one of claims 1 to 4 wherein the value of the desired setpoint is determined automatically by an optimisation algorithm. C S. 0* *f 0 S17

7. A method according to any one of claims 1 to 6 wherein each of the remaining variables is compared with respective predetermined limits, and the setpoint of the controlled variable is lowered to a reduced value, at a predetermined rate, if one or more of the remaining variables exceed their respective limits.

8. A method according to claim 7 wherein at least two different predetermined limits are set in respect of each remaining variable and the setpoint of the controlled variable is further reduced if one or more of the remaining variables exceed both of their respective limits.

9. A method according to claim 7 or claim 8 wherein the setpoint of the controlled variable is restored to its original value at a predetermined rate after both of the remaining variables have returned below their respective limits.

10. A controller for a motor-driven cone-type crusher in which a crusher gap setting between a crusher head and a crusher bowl is hydraulically controlled to prevent the motor power and pressure exerted on the crusher head from exceeding respective predetermined overload limits, the controller comprising: 0. o@ 0 18 first sensor means for monitoring a first variable related to the power drawn by the crusher motor; second sensor means for monitoring a second variable related to the pressure exerted on the crusher head; third sensor means for monitoring a third variable related to the level of material to bt crushed in the bowl; means for selecting a variable to be controlled from the first, second and third 0 variables; means for determining a desired setpoint of the controlled variable; i feed rate control means for controlling the rAte of feed of material to the crusher to maintain the controlled variable at or near S•'t the desired setpoint; and setpoint control means for effectively lowering the desired setpoint of the controlled variable if either of the remaining variables exceed respective predetermined limits, in order to prevent

19- an increase of the crusher gap above a chosen setting. 11. A controller according to claim 10 wherein the means for selecting the controlled variable is adapted to identify a dominant variable from among the first, second and third variables, and to select either the dominant variable or one of the other variables as the controlled variable. 12. A controller according to claim 11 wherein the means for selecting the controlled variable is adapted to identify the dominant variable and to L. perform the selection of the controlled variable automatically on the basis of historical data relating to the operation of the crusher. 13. A controller according to claim 10 wherein the means for selecting the corntrolled variable is adapted to allow manual selection of the controlled variable. 14. A controller according to any one of claims to 13 wherein the means for determining the desired setpoint is adapted to allow manual selection of the value of the desired setpoint, 15. 'A controller according to any one of claims to 13 wherein the means for determining the desired setpoint is adapted to determine the 910219,wpftdiskl8,26853Jet,7 20 value of the desired setpoint automatically by an optimisation algorithm. 16, A controller according to any one of claims to 14 wherein the setpoint control means is adapted to comps.re each of the remaining variables with respective predetermined limits, and to lower the setpoint of the controlled variable to a reduced value, at a predetermined rate, if one or more of the remaining variables exceed their respective limits. S* 17. A controller according to claim 16 wherein the setpoint control means is adapted to set at w least two different predetermined limits in SS. respect of each remaining variable and to further reduce the setpoint of the controlled variable if one or more of the remaining variables exceed both of their respective limits. 18. A controller according to claim 16 or claim 17 wherein the setpoint control means is adapted to restore the setpoint of the controlled variable to its original value at a predetermined rate after both of the zemaining variables have returned below their respective limits. 19. A method of controlling a motor-driven cone-type crusher substantially as herein described with -21- ref erence to Figure 2 of the accompanying drawings. A controller for a motor-driven cone-type crusher substantially as herein described with reference to Figure 2 of the accompanying drawings. *too*: M I-i .4 II I 1 111 1 1.M M O M 22

21. The steps, f eatures, compositions and ud disclosed herein or referred to icated in the specification and/or .s of this application, individually ectively, and any and all combinations of wo or more of said steps or features. 0 C 0 0 *s DATED this SIXTEENTH day of JANUARY, 1989 De Beers Industrial Diamond Division (Proprietary) Limited by DAVIES3 COLLISON Patent Attorneys for the applicant(s) *6S5 S C a S* S C S* S S S S a. S SSSSUS S S