AU2021446162A1

AU2021446162A1 - A system and method for tripper car control

Info

Publication number: AU2021446162A1
Application number: AU2021446162A
Authority: AU
Inventors: Ke Huang; Zhaocun KONG; Longhua LU
Original assignee: Sino Iron Holdings Pty Ltd
Current assignee: Sino Iron Holdings Pty Ltd
Priority date: 2021-05-20
Filing date: 2021-05-20
Publication date: 2023-07-06
Also published as: WO2022241502A1

Abstract

Various control systems and methods are disclosed herein in relation to a tripper car. The present disclosure provides a system for determining a travelled distance of a tripper car along a path, which can then be used to determine a real time location of the tripper car. The present disclosure also provides a method for braking a tripper car such that it stops at a target position. The present disclosure also provides a method for controlling movement of a tripper car in accordance with material levels at feeding points.

Description

A system and method for tripper car control

TECHNICAL FIELD

[001] The present disclosure relates to various systems and methods used for tripper car control and operation.

BACKGROUND

[002] A tripper car is a mobile transportation device widely used in construction, mining, storage facilities, and other large scale businesses. It is often used to transport and distribute raw or bulk materials to designated locations (e.g. feeding points or feeding bins) while, typically, moving on a path such as rails. Depending on the weight loading and the type of materials that a tripper car is required to transport, after it is fully loaded, the weight of a tripper car can range between a few tons and hundreds of tons.

[003] Various control methods have been developed in the past to assist with the operation of tripper car. Fixed position feeding is a widely used manual control method, which requires an operator to manually decide a target destination, and provide corresponding commands to the control system of a tripper car. As the tripper car travels, it offloads materials to designated locations. The process of offloading materials may take place as the tripper car is travelling, and/or as the tripper car stops at a designated location, such as a feeding bin, stockpiles, or a similar material container. If there is a requirement to move the tripper car to a different location, the operator sends a movement command to the control system, which then instruct the tripper car to move to the next destination. With fixed position feeding, each time the tripper car is moved or stopped, a corresponding command must be manually entered in the control system. This is a manual control process which is heavily reliant on the attendance and experience of the operator. The operator is required to be present when the tripper is operating, and any potential negligence may cause overfeeding, blocking of materials, machine damage and so on. With that said, the fixed position feeding method also provides certain advantages such as allowing accurate control of feeding load by an experienced operator, and reduced tripper car movement which then leads to reduced energy consumption and wearing of equipment.

[004] Another commonly used method involves continuously moving a tripper car between two feeding points. This is a semi-automatic feeding method in which an operator sets a start feeding point and an end feeding point, before sending out a start feeding command. During operation, the tripper car reciprocates between the start feeding and end feeding points, until a new command is provided by the operator to stop the process. This method requires less manual control than the fixed position feeding method and is often used when the volume of bulk materials which is required to be transported between two fixed locations is significant. However, a disadvantage of this method is that it consumes more energy, and causes more equipment wearing because of the reciprocating movement of the tripper car.

[005] Both methods described above require some level of operator's attention. For safety and efficiency purposes, the tripper car must run reliably and relies on the ability of the control system to detect a tripper car's real-time position accurately, so that the operator can provide suitable commands to the control system.

[006] One commonly used method to detect a tripper car's real-time position involves installing mechanical position switches, or proximity switches on the path on which the tripper car is arranged to move. When the tripper car arrives, a corresponding switch is triggered, which then sends a signal to the control system. The control system detects, or calculates the tripper car's location by scanning the status of such switches. A disadvantage with this method is that the switches are often damaged, or become unreliable in a dusty environment. Further, this method can only be used to obtain an approximate location of the tripper car due to the distributed locations of the switches themselves, and the location of the tripper car can only be obtained after the tripper car has travelled past a corresponding switch.

[007] Another method for detecting the location of a tripper car requires the installation of an encoder on a wheel or the gearbox shaft of a tripper car. The encoder is programmed to record the mechanical movement of the wheel or the gearbox shaft (e.g. rotations of the wheel), and a calculation can then be done based on the measurement recorded by the encoder. This method becomes unreliable when the wheels of the tripper car slip or slide on the rails, which happens often in practice. Over time, the measurement error could accumulate to a level which makes the measurement unacceptable. When this happens, the system must be stopped and calibrated to amend the error.

[008] Traditionally, mechanical braking is used to stop a tripper car at a designated location.

As mentioned, a fully loaded tripper car could weigh anywhere between a few tons to hundreds of tons. Due to the heavy weight, and large moving inertia, the mechanical brake is worn out rapidly and eventually may fail to stop the tripper car as desired.

[009] There is a need for an improved control system and method for operating a tripper car, which addresses or ameliorates one or more of the issues mentioned above, or to at least provide an alternative choice. [010] Any reference to or discussion of any document, act or item of knowledge in this specification is included solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these matters or any combination thereof formed at the priority date part of the common general knowledge, or was known to be relevant to an attempt to solve any problem with which this specification is concerned.

SUMMARY OF THE INVENTION

[011] In a first aspect, the present disclosure provides a system for determining a travelled distance of a tripper car along a path, between a first position and a second position, comprising: a cable, wherein a first end of the cable is placed at the first position, and a second end of the cable is coupled to the tripper car; a cable reel, for retracting or releasing a length of the cable as the tripper car is moved from the first position to the second position; a device for determining the length of the cable present between the first position and the second position, wherein the length of the cable determined equals the travelled distance of the tripper car.

[012] In one embodiment, the device measures movement of the cable reel during the retracting or releasing of the cable, and the length of the cable is determined based on the measured movement of the cable reel by the device.

[013] In one embodiment, the cable reel rotates to retract or release the length of the cable.

[014] In one embodiment, the device is an encoder operatively coupled to a rotating member of the cable reel, such that it records rotations of the rotating member as the cable reel retracts or releases the cable.

[015] In one embodiment, the device is an encoder which is used to calculate a total number of rotations as well as a degree of rotation of the rotating member.

[016] In one embodiment, the rotating member of the cable reel includes a reel shaft, and/or a turntable. [017] In one embodiment, the device is an absolute multi-turn encoder, which records mechanical movement of the rotating member of the cable reel, and generates a corresponding electrical or data signal indicative of the recorded mechanical movement of the rotating member.

[018] In one embodiment, the encoder includes a shaft and a counter, the shaft of the encoder being operatively coupled to the reel shaft, such that as the reel shaft rotates to retract or releases the cable, the encoder shaft is caused to rotate due to the coupling, and the counter records a total number of revolutions of the encoder shaft.

[019] In one embodiment, the cable reel is positioned on or in tripper car. Alternatively, the cable reel may be positioned at the first position.

[020] In one embodiment, a first calculation of the travelled distance of the tripper car is determined based on: y = R * p * [D — 2(x — 1 )d] dx where: y is distance between the first position and second position along the path, n is the number of encoder revolutions from the first position to the second position, R is the gear ratio between the encoder shaft and the reel shaft,

D is the cable reel coil outer diameter when the tripper car is at the first position, d is the diameter of the cable.

[021] In one embodiment, a first calculation of the travelled distance of the tripper car is calculated from: y = hKpΌ — Kpάh(h — 1)

V - VO n =

Res where:

Vo is the encoder reading when the tripper is at the first position,

V is the encoder reading value when the tripper car is at the second position,

Res is the encoder resolution per turn.

[022] Preferably, the travelled distance and the encoder readings have a non-linear relationship.

[023] In one embodiment, the tripper car includes one or more wheels, which rotate to move the tripper car along the path.

[024] In one embodiment, a second device is provided on a wheel of the tripper car, for recording movement of the wheel of the tripper car between the first and the second position.

[025] In one embodiment, the second device is an encoder provided on the wheel or a gearbox shaft of the tripper car.

[026] In one embodiment, a second calculation of the travelled distance of the tripper car is carried out according to a measurement provided by the second device.

[027] In one embodiment, the second calculation is carried out according to a physical dimension of the wheel, and a gear ratio of the tripper car.

[028] In one embodiment, the second calculation of the travelled distance of the tripper car is compared with the first calculation to determine a real time position of the tripper car along the path.

[029] In one embodiment, if a difference between the second calculation and the first calculation of the travelled distance exceeds a threshold value, the tripper car is stopped for maintenance purpose, for example for system recalibration or for checking whether the tripper car has slipped along the path.

[030] In one embodiment, the path between the first and second position is a non-linear path. [031] In one embodiment, the cable is a control cable which is connected to a control system of the tripper car.

[032] In one embodiment, the cable is a power cable which provides power for the tripper car.

[033] In one embodiment, the present disclosure provides a tripper car comprising a system in accordance with any of the statements in relation to the first aspect.

[034] In a second aspect, the present disclosure provides a method of controlling a speed of a tripper car, wherein the tripper car is arranged to move along a path and is set to stop at a target position on the path, comprising: determining a braking distance of the tripper car; determining a speed reduction point on the path, based on the braking distance of the tripper car; reducing the speed of the tripper car from the speed reduction point, such that its speed is reduced to zero on reaching the target position.

[035] In one embodiment, the braking distance of the tripper is calculated from braking capability of an inverter, traveling speed of the tripper car, and a weight loading of the tripper car.

[036] In one embodiment, the speed of the tripper car is controlled through a variable speed drive (VSD).

[037] In one embodiment, a driving motor of the tripper car converts from a motor state to a generator state, as the speed of the tripper car is reduced, such that excess energy is feed back to a frequency inverter.

[038] In one embodiment, the excess energy is feed back to a power grid through the frequency inverter, thereby reducing energy consumption.

[039] In one embodiment, a distance between the speed reduction point and the target position equals the braking distance of the tripper car. [040] In one embodiment, the method further includes: determining a speed reference, wherein the speed reference of the tripper car is obtained from: where:

Vmin is the minimum speed reference,

Vmax is the maximum speed reference,

S is the tripper car's current position,

Si is the tripper car's target position,

So is the braking distance.

[041] In one embodiment, a mechanical brake is applied to lock the tripper car in its target position as its speed is reduced to zero.

[042] In a third aspect, the present disclosure provides a method of providing automatic feeding to a plurality of feeding points, by one or more tripper cars which are movable along a path to feed materials to the feeding points, comprising: monitoring a level of materials at the plurality of feeding points; assigning a priority level to each of feeding points, based on the level monitored; triggering a movement command to the one or more tripper cars according to the priority levels of the plurality of feeding points.

[043] In one embodiment, a material storage container, or a stockpile is provided at each of the plurality of feeding points.

[044] In one embodiment, the material storage container is a feeding bin being arranged to receive bulk materials from the tripper car. [045] In one embodiment, a higher priority is assigned to a feeding point which has a low material level, and a lower priority level is assigned to a feeding point which has a high material level.

[046] In one embodiment, the priority level of a feeding point is decided based on the material level within a material storage container at the feeding point, as it is compared to one or more predefined setpoints.

[047] In one embodiment, the step of the triggering a movement command is only commenced after a priority level has been assigned to each of the feeding points.

[048] In one embodiment, the priority level of a feeding point is updated in real time, and the step of triggering a movement command takes place based on the real time priority level of the plurality of feeding points.

[049] In one embodiment, the priority level of a feeding point may be one of the following: high priority, if the material level is lower than a first setpoint; medium priority, if the material level is between the first setpoint and a second setpoint; low priority, if the material level is higher than the second setpoint, wherein the first setpoint is of a lower value than the second setpoint.

[050] In one embodiment, the movement command is triggered such that the tripper car is moved to a higher priority feeding point first, before it is moved to a lower priority feeding point.

[051] In one embodiment, the movement command is triggered when one of the following conditions is met: if there is a feeding point with high priority, and a material level of a current feeding point is higher than the second set setpoint; if there is a feeding point with medium or low priority, and a material level of the current feeding point is higher than a third setpoint, wherein the third setpoint is of a higher value than the second setpoint. [052] Throughout this specification, unless the context requires otherwise, the word "comprise", "comprises", or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[053] Various preferred embodiments of the present disclosure ill now be described, by way of examples only, with reference to the accompanying figures, in which:

[054] Figure 1 is a schematic diagram of a tripper car moving along a path;

[055] Figures 1 A and 1 B illustrate an example of a cable reel which is used to retract or release a length of a cable;

[056] Figure 2 shows an example of a control system interface which is used to control movement of a tripper car based on a priority level of a feeding point;

[057] Figures 3a to 3c illustrate a process logic flow of an automatic feeding method implemented in a system including a tripper car and a plurality of feeding points.

DETAILED DESCRIPTION OF EMBODIMENTS

[058] Figure 1 is a schematic diagram of a system 10 including a mobile transportation device such as a tripper car 100 being arranged to move on a path 104, along which a plurality of feeding points, such as material storage containers, stockpiles, or feeding bins 101a-101d are located. In use, the tripper car 100 is controlled to move on the path 104 to either discharge bulk materials into one of the containers, or receive materials from the containers before it is moved onto the next location. In a mining environment, this type of system is very commonly used to sort, transport and distribute bulk materials. Depending on the practical application, a tripper car could weigh between a few tons to hundreds of tons, and is generally managed by an associated control system, which controls the operation of the tripper car, including starting, stopping, controlling the speed and movement direction of the tripper car.

[059] In one embodiment, the tripper car 100 is operatively coupled to a conveyor system, which is arranged to feed raw materials to the tripper car 100. The tripper car 100 may include a compartment, or an inlet, which receives such raw materials, and diverts it to one or more discharge chutes based on a characteristic of the materials received. During operation, the conveyor system continuously feeds the materials to the tripper car 100, and as the tripper car 100 travels on its path, the materials are sorted and discharged through a suitable chute, to one or more feeding points on the path.

[060] The path 104 may include rails or any area in which the tripper car can move (some tripper cars are tracked vehicles having crawlers). The rails are structurally supported by beams, or other suitable fixtures. Accordingly, the tripper car 100 is equipped with suitable ground engaging means, for example, one or more wheels 108a, 108b so that it can travel on the path 104. The wheels 108a and 108b of the tripper are operatively coupled to one or more drive motors, which may be powered by a suitable energy source. Although Figure 1 shows the path 104 being configured in a substantially linear manner, it should be appreciated that in practice the path 104 may include turns and could be non-linear. In some applications, the path 104 could also include slopes.

[061] According to a first aspect of the present disclosure, a system which is capable of determining a travelled distance of the tripper car 100, from a first position 105 to a second position 106, is provided. The travelled distance can then be used by the control system of the tripper car 100 to determine a real-time position of the tripper car 100 in order to assist an operator or other functions of the control system.

[062] With reference to Figure 1 , the system comprises a cable 103, and an associated cable reel 107 which is designed to release or retract a length of the cable 103 according to movement of the tripper car 100. A first end of the cable 103 is placed at the first position 105, preferably fixedly or removably connected to a platform or a similar fixed structure, and the other end of the cable 103 is arranged to move with the cable reel 107 which is provided on the tripper car 100. The cable reel 107 is configured such that an unused length of the cable 103 is wound on a shaft of the cable reel 107, whereas an extended length of the cable 103 stretches evenly between the first position 103 and the second position 106 as the tripper car 100 moves.

[063] With reference to Figures 1 A and 1 B, as the tripper car 100 moves along the path 104, a shaft 111 of the cable reel 107 rotates, to release a length of the cable 103. As this process continues, a coil radius of the cable reel 107 reduces (or increases if the tripper car 100 is moving from the second position 106 to the first position 105). Either way, the length of the cable between the first and the second position will be substantially the same as the travelled distance of the tripper car 100. Therefore, by calculating the length of the cable 103 between the two positions 105 and 106, the travelled distance of the tripper car 100 can also be obtained.

[064] To calculate the length of the cable 103, an encoder device 110 is operatively coupled to the shaft 111 of the cable reel 107 to record mechanical movement of the cable reel 107. In one embodiment, the encoder 110 includes a shaft, and a counter. As the shaft 111 of the cable reel 107 rotates, the shaft of the encoder 110 is also caused to rotate due to its coupling with the cable reel 107, and its rotations are recorded by the counter. Therefore, readings of the encoder device 110 can be used to accurately calculate the rotations and/or rotational angles of the cable reel 107, in order to determine how much cable it has released or retracted. Further, knowing that each time the cable reel 107 rotates one turn, the cable reel coil outer diameter increases by two cable diameters, the travelled distance of the tripper car can be derived from the following equation: where: y is the length of the cable between the first and second positions, which is the same as the tripper car’s travelled distance,

R is the gear ratio between the encoder shaft and the cable reel shaft,

D is the cable reel coil outer diameter when the tripper car is at the first position, d is the diameter of the cable, n is the encoder turns from the first to the second position [065] The equation above can be simplified to: y = hϋpΰ — Kpάh(h — 1)

V - Vo n =

Res where, Vo is the encoder reading value when tripper car is at the anchor position,

V is the encoder reading value when tripper car is y position,

Res is the encoder resolution per turn.

[066] Figures 1 A and 1 B illustrate a simple example, in which the cable reel 107 is caused to rotate by a full turn, the reduced cable length will be equal to the circumference of the coil (p ^* D), and the winding of the cable causes the diameter of the cable reel 107 to increase from D to D+2d.

[067] In one embodiment, the encoder 110 is a multiturn absolute encoder. The advantage of using a multiturn absolute encoder is that it not only provides a measurement for the number of revolutions, but also the position within a revolution. An example of a suitable encoder is an OsiSense encoder manufactured by Schneider Electric, which supports Profibus DP data communication.

[068] Preferably, the signals generated by the encoder 110 are transmitted to the control system of the tripper car 100, using a suitable data communication protocol. In one form, the control system of the tripper car 100 includes at least one PLC (programmable logic controller) which is in data communication with a SCADA (supervisory control and data acquisition) system. The control system of the tripper car 100 is programmed such that upon receiving an encoder reading, it automatically calculates the travelled distance of the tripper car 100 using the method described above, and then uses the calculation to determine the real-time position of the tripper car 100.

[069] In practical applications, the tightness of the cable 103 may cause slight variations in the calculation of the travelled distance, and the prediction of the real time position of the tripper car, so a coefficient may be added to the equations mentioned above, which is tuned according to the actual situation. It is envisaged that with a linear distance of more than 200 meters, the actual deviation of the entire stroke is less than 0.5 meters, which is sufficient to meet the control requirements in most applications.

[070] The cable 103 could be a control cable, and/or a power cable which provides the power required to drive the tripper car 100 to move along the path 104. [071] In one embodiment, a second encoder device is attached to a wheel of the tripper car 100, and its measurement is used to derive a second calculation of the travelled distance of the tripper car 100. For example, with the measurements of the second encoder device, and a known diameter of a wheel of the tripper car, the second calculation of the travelled distance of the tripper car can be easily obtained. The second calculation may be combined, or compared with the first calculation which is derived from the cable reel encoder 110, for confirming accuracy of the results and so forth. If the discrepancy between the two calculations exceeds a predetermined threshold, for example, greater than 1 meter, then the tripper car 100 may be stopped to check for wheel slipping or other potential misalignments.

Braking control of a tripper car

[072] As mentioned previously, due to the heavy weight and large moving inertia of the tripper car 100, the mechanical brake that is used to reduce the speed of a moving tripper car is usually worn out easily. This places a challenge on stopping a tripper car at a designated location. To improve the accuracy and the efficiency of the control system, there is a requirement on the ability of the control system to park a tripper car at a target position accurately and reliably.

[073] Accordingly, in a second aspect, the present disclosure provides a method of controlling a speed of a tripper car, wherein the tripper car is arranged to move along a path and is set to stop at a target position on the path, comprising: determining a braking distance of the tripper car; determining a speed reduction point on the path, based on the braking distance of the tripper car and the target position; reducing the speed of the tripper car from the speed reduction point, such that its speed is reduced to zero on reaching the target position.

[074] Firstly, a practical braking distance of the tripper is calculated or estimated, for example, based on one or more of the following: an inverter's electromagnetic braking capability, a travelling speed of the tripper car, and a weight loading of the tripper car. For most conventional vehicles, the braking distance is usually proportional to the square of the speed of the vehicle at the instant the brakes are applied, that is, d oc V². For a tripper car that is at its full weight loading, the braking distance will be considerably greater than the braking distance when it is at a reduced weight loading. [075] Using the braking distance calculated or estimated previously, a corresponding speed reduction point can be calculated for each target position. In one form, the distance between he speed reduction point to the target position equals the practical braking distance of the tripper car.

[076] In some applications, the practical braking distance of a tripper is usually within 0.5 to 5 meters, or more preferably around 0.5 to 2 meters, and a practical braking distance may be chosen from a value that falls within this range. Alternatively, the practical braking distance can also be determined by experiments. For example, firstly, an estimated braking distance may be determined based on previous braking records. Next, a braking current and the speed reduction behavior of the tripper car are monitored, when it is fully loaded and after the braking has been applied. If the current is lower than the nominal current of the motor and the inverter, and the tripper car's speed is steadily or reliably reduced during breaking, without any slipping on the rail, then it means an appropriate level of braking power has been applied. This braking distance is then recorded and compared with the estimated braking distance, to set a more accurate practical braking distance. This process may be repeated a few times, until a suitable practical braking distance is obtained.

[077] When the tripper car arrives at the speed reduction point associated with the target position, the tripper car’s speed reference begins to ramp down until its speed is reduced to zero at the target position. In order to stop the tripper car within a reasonable time frame, it is necessary to set a minimum speed reference. When the tripper car is running at the minimum speed, the inertia becomes very low, and the speed will no longer reduce.

[078] The speed reference is calculated as follows: where:

Vmin is the minimum speed reference,

Vmax is the maximum speed reference,

S is the tripper car's current position, Si is the tripper car's target position,

So is the braking distance.

[079] The Limit function above requires that the speed reference V is always greater than Vmin and lower than Vmax. The speed reference calculated above is provided to the VSD to implement its speed reduction functions, as described further below.

[080] The braking of the tripper car, from the speed reduction point, is achieved by electromagnetic braking using a variable speed drive (VSD), operatively connected to a driving motor of the tripper car. The VSD has an electromagnetic braking function. The VSD controls the speed and torque of the driving motor by converting fixed frequency and voltage input to a variable frequency and voltage output. Preferably, the VSD is a four-quadrant inverter, also known as a regenerative inverter, meaning it is able to regenerate power and feed back to the power grid when required.

[081] During the braking process, the speed reference of the regenerative inverter decreases, and the synchronous speed of the output frequency decreases. However, due to the inertia effect of the tripper car, the rotor speed will be greater than the output frequency of the inverter. With pure mechanical braking systems, the momentum of the tripper car would be lost as heat, and represents energy wastage. In contrast, with the present invention, the motor of the tripper car converts from a motor state to a generator state, and feeds back energy to power grid through the regenerative inverter.

Automatic feeding control of a tripper car based on a material level

[082] As mentioned above, the tripper car 103 is often used to ship and distribute materials to feeding points, such as stockpiles, or storage containers such as feeding bins. In a working environment, the levels of the materials at the feeding points may be changing from time to time, and there is a desire to operate the tripper car 103 in a more efficient and cost effective manner, taking into consideration of the level of materials already at the feeding points. Moreover, there is a desire to operate the tripper car 103 automatically with reduced operator involvement.

[083] According to a third aspect of the present disclosure, there is provided a method of providing automatic feeding to a plurality of feeding points, by one or more tripper cars which are movable along a path to feed material to the plurality of feeding points, comprising: monitoring a level of materials at the plurality of feeding points; assigning a priority level to each of the feeding points, based on the level monitored, and triggering a movement command to the one or more tripper cars according to the priority levels of the plurality of feeding points.

[084] In one embodiment, a sensor is used to monitor the level of materials at the plurality of feeding points. A suitable sensor may be an ultrasonic material level sensor. Providing a sensor not only allows the control system to monitor the level of materials already present at the feeding points, it also prevents overfeeding and underfeeding, and eliminates the need of having a human operator on site. In this regard, it should be appreciated that in a mining environment, if materials overflow from a storage container such as a feeding bin, not only it is difficult to clean (considering the nature and the weight of the materials in a mining environment), it also means that the system must be stopped before it causes any further damage to equipment and staff members that are nearby.

[085] The readings of the sensors are forwarded to the control system of the tripper car 100, and a priority level is determined based on these sensor readings. A higher priority can be assigned to those feeding points where the material levels are low, and a relatively lower priority can be assigned to those feeding points where the material levels are high.

[086] In a simplest form, a priority level of a feeding point is determined based on a comparison of the material level reading from a sensor, with a predefined setpoint. Two or more setpoints could be configured by the control system or by an operator, so that a number of different priority levels are assigned to the feeding points. The example described below uses two setpoints: setpoint 1 and 2, with setpoint 1 being set at a lower value than setpoint 2. However, it should be appreciated that a greater number of setpoints and priority levels can be chosen if required. It should also be appreciated that the setpoints for each feeding point may be different, as shown in Figure 2.

[087] By way of example, the priority levels may be assigned as follows:

• High priority, if the level of material is lower than setpoint 1 ;

• Medium priority, if the level of material is between setpoint 1 and setpoint 2; and

• Low priority, if the level of material is higher than setpoint. [088] Figure 2 illustrates an example of a control system interface for a tripper car which is arranged to feed materials to 18 different feeding points. As shown, different setpoint values have been configured for the feeding points to allow more flexibility and customized feeding.

[089] Figure 2 displays the current material levels of all of the feeding points. It is evident that the material levels of feeding points 1 to 4 are the lowest (5%), as such, they will be assigned with high priority. This means that the control system will send a command to the tripper car to one of these feeding points first, if the automatic feeding method has been enabled for these feeding points, before it is sent to the other feeding points which have a higher material level.

[090] Further, the automatic feeding method may be selectively applied to a subset of all the available feeding points. In the interface shown in Figure 2, only feeding points 9 to 18 have this automatic feeding method enabled (indicated by the next to the feeding points). Feeding points 1 to 8 currently are not operating under the automatic feeding mode, which means the tripper car 103 will move pass these locations without stopping or feeding.

[091] Figures 3a to 3c illustrate a process logic flow of the automatic feeding method according to one embodiment of the present disclosure. For ease of illustration, the process has been divided into three stages: stage 1 involves scanning the current material levels of all feeding points and assigning a priority level accordingly; stage 2 involves determining a movement path for the tripper car, based on the levels monitored, and configuring a path setting for the tripper car in the control system; stage 3 involves triggering suitable movement commands in the control system in accordance with the path setting determined in stage 2. In this embodiment, a number of feeding bins are positioned at the feeding points, which receive material feeding from a moving tripper car, and a total of three setpoints are used (S1 < S2 < S3).

[092] Figure 3a illustrates a process that is used by the control system to scan a current material level for all of the feeding bins sequentially, and assign a suitable priority level accordingly. As this process is completed, each of the feeding bins will have a corresponding priority level assigned to it already.

[093] Figure 3b illustrates a process that is used by the control system to determine a movement path for the tripper car. The first step 302 requires the control system to clear the path setting which may be previously stored in the control system. Next, the control system determines where is the nearest feeding point, in the direction that the tripper car is set to move. After that, the control system checks the priority level of the nearest feeing point, and if it is of a high priority, it stores the reference of the feeding point in the path setting of the tripper car. If the feeding point is of medium or low priority, its reference is also stored in the path setting of the tripper car accordingly. As this process finishes, the tripper car's path setting has been updated to include feeding point references of high, medium and low priorities.

[094] Figure 3c illustrates a process of triggering corresponding movement commands to the tripper car, based on a material level of the current feeding point, and the path setting determined above.

[095] If the current material level is above a certain setpoint (S2), the control system triggers a movement command to move the tripper car to a high priority feeding point location, as indicated by step 303. If there is no high priority feeding point recorded in the path setting, the control system then compares the current material level with a higher setpoint (S3), and will only tripper a movement command if the current material level is higher than the higher setpoint (S3).

[096] The control system continues and repeats this process to trigger movement commands in order to execute the automatic feeding mode for the tripper car. Using this method, the tripper car can be operated entirely by the control system, with little operator’s attention. This is particularly advantageous when the tripper car is running over a long time period. Comparing to manually operated tripper car systems, the efficiency of the present system has been greatly improved. Failure rate related to a tripper car has also been significantly reduced.

[097] Although in the above description the various systems and methods have been described with reference to different embodiments, it should be appreciated that one or more combinations of the inventions mentioned in this disclosure could be implemented in a single control system in relation to a tripper car, such that its real time position is accurately determined, its braking process is more efficiently managed, and its feeding operation is automatically controlled. In a preferred embodiment, the control system of the tripper car includes a PLC, and the inventions described above are configured in the PLC as user programs. The PLC is in data communication with a SCADA system via a network, such as ethernet connection, or a wireless network. A human operator is allowed to access the PLC or the SCADA system to access or revise settings of the control system, and monitor operation of the tripper car and so forth.

Claims

1. A system for determining a travelled distance of a tripper car along a path, between a first position and a second position, comprising: a cable, wherein a first end of the cable is placed at the first position, and a second end of the cable is coupled to the tripper car; a cable reel, for retracting or releasing a length of the cable as the tripper car is moved from the first position to the second position; a device for determining the length of the cable present between the first position and the second position, wherein the length of the cable determined equals the travelled distance of the tripper car.

2. The system of claim 1 , wherein the device measures movement of the cable reel during the retracting or releasing of the cable, and the length of the cable is determined based on the measured movement of the cable reel by the device.

3. The system of claim 1 or 2, wherein the cable reel rotates to retract or release the length of the cable.

4. The system of any one of claims 1 to 3, wherein the device is an encoder operatively coupled to a rotating member of the cable reel, such that it records rotations of the rotating member as the cable reel retracts or releases the cable.

5. The system of claim 3 or 4, wherein the device is an encoder which is used to calculate a total number of rotations as well as a degree of rotation of the rotating member.

6. The system of any one of claims 3 to 5, wherein the rotating member of the cable reel includes a reel shaft, and/or a turntable.

7. The system of any one of claims 1 to 6, wherein the device is an absolute multi-turn encoder, which records mechanical movement of a rotating member of the cable reel, and generates a corresponding electrical or data signal indicative of the recorded mechanical movement of the rotating member.

8. The system of claim 4 or 5, wherein the encoder includes a shaft and a counter, the shaft of the encoder being operatively coupled to the reel shaft, such that as the reel shaft rotates to retract or releases the cable, the encoder shaft is caused to rotate due to the coupling, and the counter records a total number of revolutions of the encoder shaft.

9. The system of any one of claims 1 to 8, wherein the cable reel is positioned on or in tripper car.

10. The system of any one of claims 1 to 9, wherein a first calculation of the travelled distance of the tripper car is determined based on: where: y is distance between the first position and second position along the path, n is the number of encoder revolutions from the first position to the second position, R is the gear ratio between an encoder shaft and a reel shaft,

11 . The system of any one of claims 1 to 10, wherein a first calculation of the travelled distance of the tripper car is calculated from: y = h pϋ — Iϊpάh(h — 1)

V - VO n = — -

Res where:

Vo is an encoder reading when the tripper is at the first position,

V is an encoder reading value when the tripper car is at the second position, Res is the encoder resolution per turn.

12. The system of any one of claims 1 to 11 , wherein the travelled distance and readings of the device have a non-linear relationship.

13. The system of any one of claims 1 to 12, wherein the tripper car includes one or more wheels, which rotates to move the tripper car along the path.

14. The system of any one of claims 1 to 13, wherein a second device is provided on a wheel of the tripper car, for recording movement of the wheel of the tripper car between the first and the second position.

15. The system of claim 14, wherein the second device is an encoder provided on the wheel or a gearbox shaft of the tripper car.

16. The system of claim 14 or 15, wherein a second calculation of the travelled distance of the tripper car is carried out according to a measurement provided by the second device.

17. The system of claim 16, wherein the second calculation is carried out according to a physical dimension of the wheel, and a gear ratio of the tripper car.

18. The system of claim 16 or 17, wherein the second calculation of the travelled distance of the tripper car is compared with the first calculation to determine a real time position of the tripper car along the path.

19. The system of claim 18, wherein if a difference between the second calculation and the first calculation of the travelled distance exceeds a threshold value, the tripper car is stopped for maintenance purpose, for system recalibration or for checking whether the tripper car has slipped along the path.

20. The system of any one of claims 1 to 19, wherein the path between the first and second position is a non-linear path.

21 . The system of any one of claims 1 to 20, wherein the cable is a control cable which is connected to a control system of the tripper car, or a power cable which provides power to a drive system of the tripper car.

22. A tripper car comprising a system according to any one of claims 1 to 20.

23. A method of controlling a speed of a tripper car, wherein the tripper car is arranged to move along a path and is set to stop at a target position on the path, comprising: determining a braking distance of the tripper car; determining a speed reduction point on the path, based on the braking distance of the tripper car, and reducing the speed of the tripper car from the speed reduction point, such that its speed is reduced to zero on reaching the target position.

24. The method of claim 23, wherein the braking distance of the tripper is calculated or estimated from one or more of: braking capability of an inverter, traveling speed of the tripper car, and a weight loading of the tripper car.

25. The method of claim 23 or 24, wherein the speed of the tripper car is controlled through a variable speed drive (VSD).

26. The method of any one of claims 23 to 25, wherein a driving motor of the tripper car converts from a motor state to a generator state, as the speed of the tripper car is reduced, such that excess energy is feed back to a frequency inverter.

27. The method of claim 26, wherein the excess energy is feed back to a power grid through the frequency inverter, thereby reducing energy consumption.

28. The method of any one of claims 23 to 27, wherein a distance between the speed reduction point and the target position equals the braking distance of the tripper car.

29. The method of any one of claims 23 to 28, further including a step of determining a speed reference, wherein the speed reference of the tripper car is obtained from: where: Vmin is the minimum speed reference,

Vmax is the maximum speed reference,

S is the tripper car's current position,

Si is the tripper car's target position,

So is the braking distance.

30. The method of any one of claims 23 to 29, further comprising applying a mechanical brake to lock the tripper car in its target position as its speed is reduced to zero.

31 . A method of providing automatic feeding to a plurality of feeding points, by one or more tripper cars which are movable along a path to provide materials to the feeding points, comprising: monitoring a level of materials at the plurality of feeding points; assigning a priority level to each of feeding points, based on the level monitored, and triggering a movement command to the one or more tripper cars according to the priority levels of the plurality of feeding points.

32. The method of claim 31 , a material storage container, or a stockpile is provided at each of the plurality of feeding points.

33. The method of claim 32, wherein the material storage container is a feeding bin being arranged to receive bulk materials from the tripper car.

34. The method of any one of claims 31 to 33, wherein a higher priority is assigned to a feeding point which has a low material level, and a lower priority level is assigned to a feeding point which has a high material level.

35. The method of any one of claims 31 to 34, wherein the priority level of a feeding point is decided based on the material level within a material storage container at the feeding point, as it is compared to one or more predefined setpoints.

36. The method of any one of claims 31 to 35, wherein the step of the triggering a movement command is only commenced after a priority level has been assigned to each of the feeding points.

37. The method of any one of claims 31 to 36, wherein the priority level of a feeding point is updated in real time, and the step of triggering a movement command takes place based on the real time priority level of the plurality of feeding points.

38. The method of any one of clams 31 to 37, wherein the step of monitoring a level of materials involves monitoring the material level with an ultrasonic material level sensor.

39. The method of claim 38, wherein the method further comprises: after assigning a priority level to each of the feeding points, determining a path setting for at least one of the tripper cars.

40. The method of claim 39, wherein the path setting includes stored references of feeding points which the tripper car is arranged to move to next.

41 . The method of any one of claims 31 to 40, wherein the priority level of a feeding point may be one of the following: high priority, if the material level is lower than a first setpoint; medium priority, if the material level is between the first setpoint and a second setpoint; low priority, if the material level is higher than the second setpoint, wherein the first setpoint is of a lower value than the second setpoint.

42. The method of any one of claims 31 to 42, wherein the step of triggering a movement command is arranged such that the tripper car is moved to a higher priority feeding point first, before it is moved to a lower priority feeding point.

43. The method of any one of claims 31 to 43, wherein the movement command is triggered when one of the following conditions is met: if there is a feeding point with high priority, and a material level of a current feeding point is higher than a second set setpoint; if there is a feeding point with medium or low priority, and a material level of the current feeding point is higher than a third setpoint, wherein the third setpoint is of a higher value than the second setpoint.