EP0525230A1

EP0525230A1 - Method of and apparatus for monitoring a winding rope

Info

Publication number: EP0525230A1
Application number: EP91112756A
Authority: EP
Inventors: Bernardus Johannes Bout; Peter Charles Vickers; Lourens Badenhorst Odendaal
Original assignee: Anglo American Corp of South Africa Ltd
Current assignee: Anglo American Corp of South Africa Ltd
Priority date: 1991-07-30
Filing date: 1991-07-30
Publication date: 1993-02-03

Abstract

A method of and apparatus for monitoring a winding rope to which is attached a conveyance wherein an alarm signal is generated when the load which is borne by the rope, at a predetermined location of the rope, crosses a threshold level for a period of time which exceeds a reference time period which is proportional to the length of rope payed out.

Description

BACKGROUND OF THE INVENTION

This invention is concerned with a rope load monitoring system and particularly with the elimination of spurious or unwanted alarms which indicate that the loading of the rope has crossed a threshold level.
In a mine shaft a winding rope has a conveyance such as a cage or skip attached to it. The winding rope is moved by a winder. To optimise the operation of the winder, without placing the winding system in a dangerous condition, it is desirable to operate the winder at maximum acceleration or deceleration rates without exceeding the permissible safe loading rating of a rope.
When a conveyance is accelerated up a shaft the loading on the rope is increased and can exceed a safe upper operating level. A similar effect takes place when a conveyance is decelerated or braked when it is moving down the shaft.
On the other hand when a conveyance accelerates down a shaft the loading on the rope decreases and this can, mistakenly, be taken for a slack rope condition.
When a winder is accelerated or decelerated, upwardly or downwardly, then, due inter alia to the control characteristics of the winder, oscillations are set up in the winding rope. These oscillations manifest themselves as an increase or decrease of the measured loading of the rope at a reference point, for example at a point which is close to the winder.
The frequency of the rope oscillations varies with the length of rope which is payed out. Thus the frequency of rope oscillation is higher when the conveyance is near the surface and the rope length is short while the frequency is lower when the conveyance is near the bottom of the shaft and the length of rope, which is payed out, is relatively long.
A signal which represents the loading of the rope, measured at a reference point near to the winder, fluctuates as the rope oscillates and can cross an upper or lower alarm level for the short duration of the oscillation peak. This will cause an alarm condition to be annunciated. This type of alarm occurs under normal winding operation but is unwanted. In turn this can cause a delay in the winding operation for the cause of the alarm must be investigated so that appropriate action can be taken if necessary.
It is to be borne in mind that it is imperative that a genuine alarm condition, whether an overload or a slack rope condition, must be reacted to in the shortest possible time. When a relatively long length of rope is payed out the reaction time is not as critical as it is when the conveyance is near the surface and only a short length of rope is payed out. This is due to the degree of safety which is provided by the elasticity of the rope and which enables a longer reaction time to be tolerated if the conveyance should for example become lodged in position near the bottom of the shaft and so produce an overload or slack rope condition.

SUMMARY OF THE INVENTION

The invention is concerned with a method of and apparatus for monitoring a winding rope which enables the incidence of unwanted alarms, that are generated by rope dynamics, to be reduced.
The invention provides a method of monitoring a winding rope to which is attached a conveyance which includes the step of generating an alarm signal when the load which is borne by the rope, at a predetermined location of the rope, crosses a threshold level for a period of time which exceeds a reference time period which is proportional to the length of rope payed out.
The length of rope payed out is preferably measured with reference to the predetermined location. This location may be a point near to the winder which is used for winding the rope and thus may be at or near to the surface when the conveyance is in a shaft.
The method may include the steps of deriving a measure of the load which is borne by the rope, at the predetermined rope location, and which is due inter alia to the mass of the conveyance, the mass of the payed out length of rope, and dynamic effects which arise during winding, comparing this measure to a threshold level, measuring the period of time for which the measure crosses the threshold level, and generating the alarm signal when the measured period of time exceeds the reference time period which is proportional to the length of rope payed out.
The method may include the steps of measuring the length of rope which is payed out and of varying the reference time period so that it is directly proportional to the length of rope which is payed out. The nature in which the reference time period may depend on the length of rope which is payed out may however vary in any other appropriate or desired manner.
As used in this specification the word 'cross', when reference is made to a signal crossing a threshold level, is used to indicate the situation when the signal exceeds the threshold level, or is below the threshold level, according to circumstances. Thus an overload or a slack rope condition may be indicated.
Thus the method of the invention may be used to indicate an overload condition which occurs when the load borne by the rope exceeds a threshold level. On the other hand a slack rope condition may be detected and is indicated when the load borne by the rope is lower than a corresponding threshold level.
The reference time period is proportional to the length of rope which is payed out by the winder. Thus the reaction time to generate an alarm signal is relatively long when a substantial length of rope is payed out and decreases as the payed out length of rope shortens.
The invention also extends to apparatus for monitoring a winding rope to which is attached a conveyance which includes means for generating a first signal which is dependent on the load borne by the rope at a predetermined location of the rope, means for comparing the first signal to a threshold level and for generating a second signal when the first signal crosses the threshold level, means for monitoring the length of rope which is payed out by the winder, means for generating a reference time period which is proportional to the payed out rope length, and means for generating an alarm signal when the time period for which the second signal is generated exceeds the reference time period.
The reference time period may be generated in any appropriate way. In one form of the invention a pulse train is generated at a frequency which is inversely proportional to the length of payed out rope, the pulses are counted, and the reference time period is indicated when the pulse count reaches a predetermined number.
As used in this specification the word 'rope' includes a cable or other flexible elongate element from which a conveyance may be suspended.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a block diagram of an alarm annunciator according to one form of the invention, and
Figure 2 depicts the manner in which the frequency of a pulse train generated in the annunciator of Figure 1 varies with payed out rope length.

DESCRIPTION OF PREFERRED EMBODIMENT

Figure 1 of the accompanying drawings illustrates an alarm annunciator which is used to eliminate or reduce unwanted alarms that are generated by dynamic effects on a winder rope from which a conveyance is suspended, for example, in a shaft. The alarm annunciator is intended to cater for genuine alarm conditions which may arise, taking into consideration the critical time which is required to react safely thereto.
The function of the annunciator is described hereinafter with reference to monitoring the load which is borne by a winder rope from which is suspended a cage or a skip, in a shaft. This is given merely by way of example for the use of the annunciator is not confined to this particular application.
Referring to Figure 1 the annunciator is designated by the reference numeral 10. Connected to input terminals 12, 14, 16 and 18 of the annunciator are modules 20, 22, 24 and 26 respectively, which are known per se.
The module 20 provides a signal which is dependent on the length of rope payed out from the winder.
The module 22 is used to measure the load which is borne by the rope, and preferably this load is measured at or near the surface, i.e. near the winder, and is substantially equal to the sum of the mass of the conveyance, the mass of the payed out rope length, and loading induced in the rope by dynamic effects which arise when the rope is payed out or wound in. The module 22 provides a signal which is proportional to the load imposed on the rope as well as the load imposed on the rope by the dynamic effects which arise when the rope is payed out or wound in.
The module 24 provides a signal which indicates when the brakes of the winder are on or off.
The module 26 provides a signal which is dependent on the speed of the winder.
The annunciator includes two output terminals 28 and 30 which respectively are connected to a data logger, not shown, and to an alarm relay, also not shown.
The annunciator includes an inverting amplifier 32 the gain of which is adjustable by means of a potentiometer 34, an inverting summing amplifier 36, the gain of which is adjustable by means of a potentiometer 38, a voltage controlled oscillator 40, a low pass filter 42, a level or threshold detector 44, a logic gate 46. a counter 48, a logic circuit 50 which has inputs from the counter 48, the threshold detector 44, and the input terminals 16 and 18, a buffer 52 which has its input connected to the output of the logic circuit 50 and its output connected to the output terminal 28, and a relay driver 54 which is connected between the logic circuit 50 and the output terminal 30.
The accompanying drawings do not illustrate the conveyance, the rope from which the conveyance is suspended, nor the winder. These aspects are conventional and are known per se.
When the conveyance is positioned at surface the length of the payed out rope is effectively zero. A signal which is produced by the module 20 is applied to the input terminal 12 and the potentiometer 38 associated with the summing amplifier 36 is adjusted to set the highest output frequency, f2, of the voltage controlled oscillator 40 to the required value.
The conveyance is then moved to the lowest level in the shaft. The signal which is input to the terminal 12 varies accordingly and the potentiometer 34 which is associated with the variable gain amplifier 32 is adjusted to set the lowest output frequency f1 of the voltage controlled oscillator 40 to the required value.
The frequency range of the oscillator 40 is shown in Figure 2 as a function of the payed out length of the rope. It is apparent that the frequency of the oscillator is inversely proportional to the payed out rope length and varies accordingly as the conveyance moves up and down the shaft.
The load which is borne by the rope is measured by the module 22 and the signal produced by this module, after it has been conditioned in the filter 42, is input to the level detector 44 where it is compared to a reference signal, determined in accordance with known criteria, which is input to the level detector from a potentiometer 56.
Assume that the annunciator is intended to detect an overload condition. When an overload condition arises this is indicated by the level detector 44 which outputs an appropriate signal to the logic gate 46, the counter 48, and the logic circuit 50.
The logic gate 46 is enabled and pulses produced by the voltage controlled oscillator 40 are counted by the counter 48. When the count in the counter reaches a predetermined value, which is fixed taking the characteristics of the winder and shaft into consideration, the counter generates an output signal which enables the logic circuit 50 provided signals are present at the terminals 16 and 18 indicating respectively that the winder brakes are off and that the winder speed is below a predetermined speed.
When the prescribed conditions exist and the predetermined count is reached an alarm signal is generated by the logic circuit 50 and applied to the buffer 52 and relay driver 54. The buffer produces a signal, at the terminal 28, which is supplied to a data logger while the relay driver 54 generates a signal which is available at the terminal 30 and which is used to activate an appropriate alarm and to initiate appropriate action.
Once the alarm condition has been cleared the output signal from the threshold detector 44 changes indicating that an overload condition no longer exists. The logic gate 46 is disabled as is the logic circuit 50, and the counter 48 is reset to zero.
If the alarm condition clears before the counter 48 reaches the predetermined count then the logic gate 46 is disabled. This prevents the output pulses from the voltage controlled oscillator 40 from further advancing the counter 48. The counter is then reset to zero and the logic circuit 50 is kept disabled. The alarm signal from the threshold detector 44 cannot therefore be routed to the output drivers 52 and 54.
The system thus enables an alarm condition, as indicated by the level detector 44, to be tolerated for a period of time which is proportional to the length of rope which is payed out at that moment. As has been described the length of rope is used to control the frequency of oscillation of the oscillator 40 and its frequency is inversely proportional to the rope length. Thus the time interval between successive pulses output by the oscillator increases as rope length increases and this means that the counter 48 reaches its predetermined count in a time interval which is proportional to the payed out length of rope.
The predetermined time interval which is effectively generated by the counter 48 is longer than the period for which an alarm condition is generated by dynamic effects on the rope during winding. Thus dynamic effects can be catered for and no alarm is generated when the load on the rope briefly exceeds the overload rating of the rope. On the other hand if this rating is exceeded for more than the predetermined period an alarm condition is generated.
The invention has been described with reference to detecting an overload condition. Similar conditions prevail in the event a slack rope condition is to be detected. Thus two circuits of the kind shown in Figure 1 are used to detect overload and slack rope conditions respectively. In the latter case the load of the rope is compared by the level detector 44 to a minimum level generated for reference purposes by the potentiometer 56. If the load borne by the rope is below the minimum level for a period which is less than a predetermined time delay, which is proportional to the payed out length of rope, then no alarm signal is generated and the slack rope condition is attributed to dynamic effects. On the other hand if the slack rope condition endures for more than the predetermined time period then a genuine alarm condition is indicated and, in a manner analogous to that already described, alarm signals are generated at the terminals 28 and 30.
Thus, after an alarm has been initiated reaction to that alarm takes place only after a predetermined time interval has elapsed. This time interval is dependent on the length of rope which is payed out at the moment. The longer the length of rope that is payed out the longer is the reaction time to the alarm condition. The reaction time becomes progressively shorter as the conveyance suspended from the rope moves towards the surface and, at surface, an alarm condition is reacted to immediately. As has been pointed out a longer reaction time can be tolerated when the conveyance is far from surface for the elasticity of the longer winding rope provides a degree of safety.
When overload and slack rope conditions are to be detected then it is not necessary fully to duplicate the circuitry shown in Figure 1, for detecting each condition. The annunciator shown in Figure 1 can be used, for example, to detect an overload condition and the portion of the annunciator enclosed in a dotted line 58 is duplicated for the slack rope detector. Connections are made between the annunciators, as appropriate, and as is indicated by the connection points designated 60, 62, 64 and 66 respectively.

Claims

1. A method of monitoring a winding rope to which is attached a conveyance which is characterized in that it includes the step of generating an alarm signal when the load which is borne by the rope, at a predetermined location of the rope, crosses a threshold level for a period of time which exceeds a reference time period which is proportional to the length of rope payed out.

2. A method according to claim 1 characterized in that the length of rope which is payed out is measured with reference to the predetermined location.

3. A method according to claim 1 or 2 characterized in that the conveyance is in a shaft and the reference location is at or near to surface.

4. A method according to any one of claims 1 to 3 which is characterized in that it includes the steps of deriving a measure of the load which is borne by the rope, at the predetermined rope location, and which is due inter alia to the mass of the conveyance, the mass of the payed out length of rope, and dynamic effects which arise during winding, comparing this measure to a threshold level, measuring the period of time for which the measure crosses the threshold level, and generating the alarm signal when the measured period of time exceeds the reference time period which is proportional to the length of rope payed out.

5. A method according to any one of claims 1 to 4 which is characterized in that it includes the steps of measuring the length of rope which is payed out and of varying the reference time period so that it is directly proportional to the length of rope which is payed out.

6. A method according to any one of claims 1 to 5 characterized in that it is used to indicate an overload condition which occurs when the load borne by the rope exceeds a threshold level.

7. A method according to any one of claims 1 to 6 characterized in that it is used to detect a slack rope condition which occurs when the load borne by the rope is lower than a corresponding threshold level.

8. Apparatus for monitoring a winding rope to which is attached a conveyance which is characterized in that it includes means (22) for generating a first signal which is dependent on the load borne by the rope at a predetermined location of the rope, means (44) for comparing the first signal to a threshold level and for generating a second signal when the first signal crosses the threshold level, means (20) for monitoring the length of rope which is payed out by the winder, means (40,48) for generating a reference time period which is proportional to the payed out rope length, and means (46,48,50) for generating an alarm signal when the time period for which the second signal is generated exceeds the reference time period.

9. Apparatus according to claim 8 characterized in that the means (40,48) for generating the reference time period includes means (40) for generating a pulse train at a frequency which is inversely proportional to the length of payed out rope, and means (48) for counting the pulses, the reference time period being indicated when the pulse count reaches a predetermined number.