CA2168171A1

CA2168171A1 - Oscillation-damping control of motor torque for mine hoist

Info

Publication number: CA2168171A1
Application number: CA002168171A
Authority: CA
Inventors: Johann Galic; Claes Kumpulainen
Original assignee: Asea Brown Boveri AB
Current assignee: ABB AB
Priority date: 1995-01-30
Filing date: 1996-01-26
Publication date: 1996-07-31
Also published as: CN1134393A; SE9500316L; SE503755C2; ZA96613B; CN1071699C; SE9500316D0

Abstract

A method and a device, in a mine hoist, for damping the vertical oscillations which may arise in the skip/skips (8, 9) of the mine hoist during different operating conditions.
According to the invention, with the aid of a Kalman filter in the form of an estimator (12) based on a state model of the mine hoist, estimated values of the speed (z1, z2) of the skip/skip may be obtained. with access to these estima-ted values, the torque control, included in the speed con-trol of the mine hoist and superimposed on the torque which is required from the speed controller (1) via a torque control generator (13), may be given a torque addition which acts in such a way that, as soon as differences arise between the speed of the rope drum nltr of the mine hoist and the estimated speeds of the skips, the tendencies to oscillations are counteracted and reduced after a short building-up process (Figure 5).

Description

k -,~ ~1 ;, ~"~

Oscillation-damDina control of motor torque for mine hoist TECHNICAL FIELD

Ore which is recovered in mines is transported up to the surface with the aid of so-called mine hoists. The ore mining often occurs at very large depths which may amount to several thousand metres. Because of the long ropes which are then needed between the rope drum and the skip (or conveyance) of the mine hoist, problems with oscillations of the skip in the vertical direction often arise. This is due to the ropes behaving as springs. The present invention suggests a method and a device for preventing the occurrence of such oscillations.

BRIEF DESCRIPTION OE THE DRAWINGS

Figure 1 shows speed control of a mine hoist according to the state of art.
Figures 2 and 3 show ramp functions for reducing the risk of oscillations of the skip during start, stop, etc.

Figure 4 shows a physical model of a mine hoist.

Figure 5 shows a control system for a mine hoist according to the invention Figure 6 shows an embodiment of a control system for a mine hoist according to the invention BACKGROUND ART, THE PROBLEM

To place the invention in its proper context, a brief description of mine hoists and the problems which may arise both during normal hoist movement and during starting and normal retardation, as well as during emergency braking of the load, will first be given.

`- 21 681 71 There are two types of mine hoists which are usually referred to as drum hoists and friction hoists.

Drum hoists comprise (a) mine hoists with a rope drum where the rope is wound onto the drum when the skip goes up, and (b) mine hoists with double rope drums with one skip each and where the ropes are also wound onto the rope drum and are so arranged that, when one of the skips is furthest down in the shaft, the other skip is furthest up in the shaft.

In friction hoists, one or more ropes in the form of steel wires are suspended freely in separate grooves over the rope drum. From the rope ends on one side, the skip in which the ore is loaded is suspended. From the rope ends on the other side, another skip or counterweight is suspended.
This means that the only thing which prevents the ropes from slipping or sliding over the drum is the friction between ropes and drum grooves. To keep the total suspended rope mass on both sides of the rope drum constant, balance ropes are arranged between the under sides of the skip and the counterweight.

To be able to secure the mine hoist during a standstill, that is, to so-called holding braking, various electri-cally/hydraulically/pneumatically controlled mechanical brake systems are used, which are applied to the rope drum or to the ropes themselves. These mechanical brakes are also used for emergency braking of the mine hoist. In a ~() commonly used mechanical brake system, the side members of the rope drum are each provided with an annular brake disc and the braking is performed with the aid of hydraulic disc brakes with brake blocks on both sides of the brake disc.
In another commonly used brake system, the braking is performed with the aid of drum brakes.

A drum hoist with double rope drums is described, inter alia, in the ABB Pamphlet 3ASMOlC200, 1993-06, ABB Mine Hoist. As is clear from the pamphlet, the drive system may consist of an a.c. or a d.c. drive system. The drive systems are designed to minimize dynamic strains in the ropes by giving soft changes both as regards speed and motor torque. Further, it is clear from this pamphlet that rope tension meters may be applied to each rope. Rope tension measurement may, of course, also be used in friction hoists. This permits a possibility of continuously monitoring the rope tension, among other things to check slackening of some rope. In addition, the rope tension measurement is used during starting to influence the motor torque to counter the unbalance which prevails between the rope tension on the skip side and on the counterweight side. This means that, when the brakes release after the skip has been filled with ore, the drive motor may be given such a torque that the load does not drop but is, instead, given a smooth acceleration with a reduced risk of introducing oscillations in the ropes.

The problems with vertical oscillations of the skip may arise both in a drum hoist and in a friction hoist. The risk of oscillations arising increases with the length of the ropes, that is, when the depth of the mine shaft increases. It is primarily during loading/unloading of a load, during starting/stopping of a driving cycle and during emergency braking that such oscillations may arise.

Independently of which electric drive system is used for driving the rope drums, the operation comprises an external speed control with an internal current or torque control of the motor. A typical scheme for such control with a speed controller 1, which compares the desired speed of the rope drum, nref~ with the actual speed of the rope drum nltr, and which delivers a signal MM corresponding to the reference of the torque control, a torque controller 2 and a drive system 3 according to the prior art is shown in Figure 1. Example of such controls are described, inter alia, in an article entitled ~Control Systems for Mechani-cal Brakes for Emergency Stops", published in connection with MINE HOISTING 93, Second International Conference, 28-30 June 1993, pp 2.3.1-2.3.6, The Royal School of Mines, London. To avoid oscillations in the ropes in connection with starting, stopping and emergency braking of the load, "S"-shaped reference signals for the speed control both during a starting and a stopping cycle are also used in accordance with the prior art. A reference procedure for the speed control for a stop is clear from Figure 2. Figure 3 shows a corresponding retardation reference for the torque control for a stopping cycle. The retardation begins with a linearly increasing ramp when then changes into a constant retardation and which, at the end of the retarda-tion process, changes in a ramp decreasing linearly towards zero.

In spite of the above-mentioned measured with a smooth start/stop etc., it has been difficult to prevent the occurrence of oscillations in the ropes. It has therefore been necessary, inter alia, to have such a smooth start and retardation that it has had an injurious effect on the duration of the running cycle. In addition, especially in case of deep mine shafts and correspondingly long ropes, disturbances of various kinds during transport of a load at a constant speed may also introduce oscillations. In drum hoists with two rope drums, oscillations in the skip on one of the rope drums may initiate oscillations of the skip on the other rope drum. Therefore, there is a considerable need of a method which, independently of the stage in the running cycle, as soon as a tendency of oscillations arises, can initiate measures to prevent a development of the oscillation tendencies.

As will have been clear from the above, these oscillations may arise because the ropes behave as springs. Equations for the behaviour of suspended springs belong to classical mechanics. Because of the length of the ropes, however, when carefully studying these oscillations, distributed rope masses should be taken into consideration. As a technical base for describing the invention, a differential equation system for an aggregated model will be briefly s described, wherein the rope is allowed to be approximated by point masses separated by massless springs and with the rope weight included in the skip and the counterweight.
Such a model is shown in Figure 4 which relates to a friction hoist. The equation system is based on the following parameters:
Fk1,Fk2 - spring forces on skip and counterweight 11,12 - actual rope length v1,v2 - speed of skip and counterweight u - applied torque, input signal to the system m1,m2 - mass of skip including load and rope mass on skip side and mass of counterweight including rope mass on counterweight side f1,f2 - viscous damping in ropes k1,k2 - spring constants of ropes r - radius of rope drum c - bearing friction J - moment of inertia for motor rotor with shaft and rope drum ~ - angular velocity of rope drum The differential equations will then be as follows:

~ 21 681 71 v, =--(f~(r~ - v, ) + Fk, - mlg) m, V2 =--( f 2 (ro - V2 ) + Fk2 - m2g) Fk, = k, (r~ - v, ) Fk2--k2 (r~)--v2 ) ~ = J (u - CCI~ - fir(r~ - vl) - f2r(r~ - V2) - rFkl - rFk2) It is part of the state of the art to transfer such a model to a state model wherein Xl = Vt X2 = V2 X3 = Fk~
X4 = Fk2 x5 = ~, are allowed to be the states in the model. This gives the system on a state form according to x(t) = A-x(t) + B-u(t) y(t) = C-x(t) + D-u(t) with system matrices defined on the basis of the described differential equations, for example where - f' O1 o fi r ml ml ml O - f.'O 1 f2 r A = m, m, m, -k, on () kl r f, r f, r r r c+f, r~+ f, r~
J J J J J

To be able to handle and to apply measures which prevent the occurrence of such oscillations, respectively, it would be desirable to have continuous access to the speed of the skip. However, this speed is not directly measurable or definable. If, on the other hand, the speed of the skip were known, it should be possible, by determining the difference between the speed of the rope drum and the speed of the skip, to apply stabilizing measures. However, the differential equations for a mine hoist described above give no direct indication as to how this problem should be solved.

SUMMARY OF THE INVENTION, ADVANTAGES

As mentioned above, the rope tension may be determined with the aid of tensile force-measuring devices in each rope.
With access to the rope tension, a mathematical state model of a mine hoist, for example according to the following equations (1), (2) och (3), may be utilized, according to the invention, for estimating the speed of the skip x(t) = A-x(t) + B-u(t) +N-el (1) y(t) = C-x(t) + e2 (2) z(t) = H-x(t) (3) Here, x(t) represents a state vector for the mine hoist, x(t) the derivative-of the state vector, y(t) the available measurement signal from the rope tension, and z(t) the desired speed of the skip. In this equation system, A, s, N, C and H are matrices which may be determined starting from the data of the mine hoist in question, for example from the differential equation system described. Further, el and e2 represent disturbances with an intensity Rl and R2, respectively, and with a cross spectrum equal to R12.

Based on such a state model, the following Kalman filter may be defined x(t) = A-x~t) ~ B-u(t) + K(y(t) - C-x(t)) (4) z(t) = H-x(t) (5) where x(t) is the estimated value of x(t), x(t) is the estimated value of x(t), u(t) is the applied torque, and z(t) is the estimated speed of the skip. K is an amplification according to:

K = (p cT + N R12) ~

Generally, according to known linear algebra, a matrix with an exponent ~T~ is a transponant of the respective matrix.
P is the posive semidefinite solution of the generally known matrix equation of a Kalman filter, that is A-P + P-AT + N-Rl-NT-(P-CT + N-R12)- ~ (P-CT + N-R12)T =0 The state vector x(t) mentioned above may be adapted to the mine hoist used in such a way that it may describe different types of mine hoists. It may, for example, describe a mine hoist with two rope drums, whereby the estimated speeds z(t)1 and z(t)2, respectively, of the two skips may be obtained.

With the scope of the invention, the Kalman filter may contain a less aggregated state model than that described by the equations (1), (2) och (3), for example a more advanced state model with several point masses.

Figure 5 shows a diagram, according to the invention, of the principle of the speed control of a mine hoist, compri-sing a drum hoist with two rope drums. The control circuit comprises, in conventional manner and in accordance with Figure 1, a speed controller 1 which compares the desired speed of the rope drum, nref~ with the actual speed of the rope drum, nltr, a torql~e controller 2 with feedback of the actual motor torque M, and a drive system 3. The speed con-troller may be designed in different ways and with diffe-rent characteristics depending on the static and dynamic requirements which are imposed on the speed control. Here, as in Figure 1, it is assumed that the output signal of the speed controller is equal to MM. It is further assumed that either nref or the speed controller may comprise the "S"-shaped limits and ramp functions which have been described above to reduce the risk of oscillations and which are part of the prior art.

Figure 5 also shows the two rope drums 4 and 5 with their respective ropes 6 and 7 as well as the skips 8 and 9. The rope tension Sl in the rope 6 is measured in a measuring device 10 and the corresponding rope tension S2 in the rope 7 is measured with the measuring device 11.

What is new for the speed control according to the inven-tion is that signals from the rope tension measurement and the actual speed nltr of the rope drum are utilized as input signals to an estimator 12 in the form of a Kalman filter based on some state model of a mine hoist, for example according to the above-mentioned model according to equations tl), (2) and (3) and which, according to the above reasoning, may continuously deliver signals which correspond to the estimated values of the speeds of the two skips, that is, Zl and Z2, respectively.

~() Further, as will be clear from Figure S, according to the invention, a torque reference generator 13 is used which delivers the desired torque reference Mref to the torque control of the drive system. Input signals to the torque generator consist of the output signal MM of the speed controller according to the above, the estimated values of the speeds Zl and Z2 of the skips, and the actual speed nltr of the rope drum. The torque reference is now formed according to:

- ~- 21 681 71 1"
M",f = MM + Pl (n~,r--Z, ) + P2 (nllr--Z2) The torque reference generator 13 comprises, for the mine hoist in question, the weighting factors P1 and P2 which are determined depending on the actual operating situation, that is, end position, centre position, acceleration/retardation, etc.

By imparting to the drive system 4 a torque reference according to the above, the torque control included in the drive system, superimposed on the torque required via the speed controller, will have a torque addition which acts in such a way that, as soon as differences arise between the speed of the rope drum and the estimated speed of the skips, the tendencies to oscillations are counteracted and reduced after a short building-up process. The torque addi-tion will thus enter into operation indpendently of whether the oscillation tendencies are introduced because of loading/unloading of a load or during start/stop of a 2() running cycle.

The advantages of this system, which significantly reduce the dynamic stresses which arise when the skip oscillates, in addition to giving a reduced rope oscillation, are also a reduced risk of rope slipping in a friction hoist.
Another and very important advantage with a reduced dynamic load is that the safety factor for the rope may be lowered, which permits the payload of the mine hoist to be increased. This is particularly important at very large ~() hoist depths.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 5 shows the speed controller 1, the torque con-troller 2, the estimator 12, as well as the torque reference generator 13 in the form of blocks. However, it is self-evident that state models and Kalman filters with current technique are implemented in the form of programs Il in a calculating means, preferably in a computer. The same also applies to the controllers which are used in this type of control equipment. The hardware which is used consists of the power converter of the drive system, the motor, the rope drum, the skips, etc.

An embodiment of the invention could, therefore, be descri-bed based on Figure 6. Implemented in the calculating means 14 are thus programs for reference functions in the form of 10 U S n - and ramp functions, the n-controller 1, the Mref-generator 13, the torque controller 2, and the estimator 12. Signals to the computer are obtained from the requested maximum speed nref~ the actual speed of the rope drum nltr, the torque feedback M, and the signals SI and S2 from the rope tension measuring devices 10 and 11. The output signal from the computer will then be the torque reference Mref to the drive system 3. Otherwise, Figure 6 shows the rope drums 4 and 5, the ropes 6 and 7, and the skips 8 and 9.

The description of the invention and Figure 5 relate to friction hoists with two rope drums and two skips, respec-tively. The principle of the control according to the invention may, of course, be applied also to friction hoists with one rope drum and one skip, and also to drum hoists.

From a purely practical point of view, the estimator is adapted such that, if the rope tension signals disappear because of an interruption or otherwise, or if the estima-tor quite obviously deliver incorrect signals, the estima-tor will deliver signals which are estimated to correspond to the speed of the skip/skips.

Claims

1. A method, in a mine hoist, for damping the vertical oscillations which may arise in the skip/skips (8, 9) of the mine hoist during different operating conditions, wherein the mine hoist comprises a speed control of the rope drum/rope drums (4, 5) of the mine hoist, and wherein the speed control comprises a speed controller with an output signal (MM), and wherein the speed control has an internal torque control consisting of a torque controller (2) and a drive system (3), and wherein the skip/skips are suspended from ropes (6, 7) between the rope drum/rope drums and the skip/skips, and wherein the ropes are provided with rope tension measuring devices (10, 11) for determining the rope tension S1 and S2 in the ropes, and wherein the method is characterized in that the internal torque control of the speed control comprises an estimator (12) in the form of a Kalman filter based on a state model of a mine hoist, and that the estimator is supplied with the signals S1 and S2 from the rope tension measuring devices as well as a signal corresponding to the speed nltr of the rope drum, and that the output signals of the estimator consist of signals corresponding to estimated values of the speed (?1, ?2) of the skip/skips, and a torque reference generator (13) which is supplied with the output signal MM of the speed controller, estimated values of the speed (?1, ?2) of the skip/skips, as well as a signal corresponding to the speed nltr of the rope drum to form a torque reference Mref to the drive system Mref = Mn + P1(n?-?1)+P2(n?-?2) where P1 and P2 are given weighting factors.

2. A method according to claim 1 for damping, in a mine hoist, the vertical oscillations which may arise in the skip/skips (8, 9) of the mine hoist during different operating conditions and which is characterized in that the Kalman filter is determined according to ?(t) = A?(t) + Bu(t) + K(y(t) - C?(t)) (4) ?(t) = H?(t) (5) ?(t) is the estimated value of x(t) ?(t) is the estimated value of ?(t), ?(t) is the estimated speed of the skip/skips K = (pcT + NR12)R?

P is the positive semidefinite solution to the matrix equation of the Kalman filter AP + PAT + NR1NT - (PCT + NR12) R?(PCT + NR12)T
= 0 and which is based on a state model of the mine hoist according to ?(t) = Ax(t) + Bu(t) +Ne1 (1) y(t) = Cx(t) + e2 (2) z(t) = Hx(t) (3) x(t) is a state vector for the mine hoist ?(t) is the derivative of the state vector u(t) as the applied torque y(t) are available measured signals from the rope tension/rope tensions z(t) is the speed of the skip/skips A, B, N, C and H are matrices which are determined on the basis of the data of the actual mine hoist, and e1 and e2 are disturbances with intensities R1 and R2, respectively, and with a cross spectrum equal to R12

3. A device for carrying out the method according to claim 1 for damping, in a mine hoist, the vertical oscillations which may arise in the skip/skips (8, 9) of the mine hoist during different operating conditions, wherein the mine hoist comprises a speed control of the rope drum/rope drums (4, 5) of the mine hoist, and wherein the speed control with a control signal in the form of a speed reference nref has a speed controller (1) with an output signal (MM) and an internal torque control (2) and a drive system (3), and wherein the skip/skips (9, 10) are suspended from ropes (6, 7) between the rope drum/rope drums and the skip/skips, and wherein the ropes are provided with rope tension measuring devices (10, 11) for determining the rope tension S1 and S2 in the ropes, characterized in that in a calculating means (14) there are implemented programs for a speed controller (1) comprising the speed refernce functions of the mine hoist with the output signal MM, an estimator (12) for estimating the speed ?1 and ?2 of the skips, a torque reference generator for forming a signal Mref = Mm + P1(n?-?1) + P2(n?-?2) where P1 and P2 are given weighting factors, a torque controller (2) for delivering an input signal to the drive system, and that the input signals of the calculating member consist of the speed reference nref, a feedback signal from the actual torque M of the drive system, the speed nltr of the rope drum/rope drums, and signals from the rope tension measuring devices corresponding to the rope tension in the ropes.

4. A device according to claim 3 for damping, in a mine hoist, the vertical oscillations which may arise in the skip/skips of the mine hoist, characterized in that the Kalman filter is arranged according to ?(t) = A?(t) + Bu(t) + K(y(t) - C?(t)) (4) ?(t) = H?(t) (5) ?(t) is the estimated value of ?(t) ?(t) is the estimated value of ?(t), ?(t) is the estimated speed of the skip/skips K = (pcT + NR12)R?

P is the positive semidefinite solution to the matrix equation of the Kalman filter AP + pAT + NR1NT - (PCT + NR12)R?(PCT + NR12)T
= 0 and that the Kalman filter is based on a state model of the mine hoist according to ?(t) = Ax(t) + Bu(t) + Ne1 (1) y(t) = Cx(t) + e2 (2) z(t) = Hx(t) (3) x(t) is a state vector for the mine hoist ?(t) is the derivative of the state vector u(t) is the applied torque y(t) are available measured signals from the rope tension/rope tensions z(t) is the speed of the skip/skips A, B, N, C and H are matricese which are determined on the basis of the data of the actual mine hoist, and e1 and e2 are disturbances with intensities R1 and R2, respectively, with a cross spectrum equal to R12.