阅读说明：本技术 一种双起重机的实时调度-控制级联系统及方法 (Real-time scheduling-control cascade system and method for double cranes ) 是由 王耀宗 胡志华 黄永付 于 2019-10-17 设计创作，主要内容包括：本发明公开了一种双起重机的实时调度-控制级联系统及方法,该系统包括：调度层,接收双起重机调度的任务信息并进行重组调度和实时优化,获得调度计划；控制层,输入端与调度层级联结构连接,输出端与起重机的主电机连接,根据调度计划进行计算,生成最佳控制值,并根据所述最佳控制值实时调控起重机。此系统解决了调度计划的实时性差、效率低和控制系统的准确性和平稳性差的问题,实现了调度计划与控制方案参数共享,相互反馈协调,保证了故障发生时系统保持持续作业的平稳性和准确性。(The invention discloses a real-time scheduling-control cascade system and a method of a double crane, wherein the system comprises: the scheduling layer receives task information scheduled by the double cranes, performs recombination scheduling and real-time optimization, and obtains a scheduling plan; and the input end of the control layer is connected with the dispatching hierarchy connection structure, the output end of the control layer is connected with a main motor of the crane, calculation is carried out according to a dispatching plan, an optimal control value is generated, and the crane is regulated and controlled in real time according to the optimal control value. The system solves the problems of poor real-time performance and low efficiency of the dispatching plan and poor accuracy and stability of the control system, realizes parameter sharing and mutual feedback coordination of the dispatching plan and the control scheme, and ensures that the system keeps the stability and the accuracy of continuous operation when a fault occurs.)

1. A real-time dispatch-control cascade system for dual cranes, the system comprising:

the scheduling layer receives task information scheduled by the double cranes, performs recombination scheduling and real-time optimization, and obtains a scheduling plan;

and the input end of the control layer is connected with the dispatching hierarchy connection structure, the output end of the control layer is connected with a main motor of the crane, calculation is carried out according to the dispatching plan, an optimal control value is generated, and the crane is regulated and controlled in real time according to the optimal control value.

2. The real-time scheduling-control cascading system of the dual crane as claimed in claim 1, wherein the scheduling layer comprises:

the task receiving module is used for receiving task information needing to be scheduled by the double cranes;

the input end of the detection module is connected with the task receiving module and is used for detecting whether the task information responds to the dynamic task;

the input end of the recombination module is connected with the first output end of the detection module, and the task information after responding to the dynamic task is recombined and scheduled;

and the first input end of the optimization module is connected with the output end of the recombination module, the second input end of the optimization module is connected with the second output end of the detection module, the output end of the optimization module is connected with the control layer, and task information which completes recombination scheduling after no response dynamic task/response dynamic task is optimized in real time.

3. The real-time scheduling-control cascading system of the dual crane as claimed in claim 1, wherein the control layer comprises:

the input end of the position sensor is connected with the crane, and the real-time position information of the crane is monitored in real time;

the first input end of the selection module is connected with the cascade structure of the optimization module, the second input end of the selection module is connected with the position sensor, the scheduling plan is selected, the optimal set value is selected, deviation calculation is carried out according to the optimal set value and the real-time position information, and the optimal control value is generated;

the input end of the controller is connected with the selection module, the output end of the controller is connected with a main motor of the crane, the controller controls the crane according to the optimal control value and outputs a real-time manipulated variable;

the main motor of the crane is connected with the crane, and the crane is driven to move in real time according to the real-time manipulated variable; the selection module, the controller, the main motor of the crane, the crane and the position sensor are sequentially connected to form a closed loop negative feedback loop.

4. The system as claimed in claim 3, wherein the control layer further comprises an adaptive controller, the input end of the adaptive controller is connected to the position sensor, the output end of the adaptive controller is connected to the controller, and the adaptive controller monitors whether the crane is disturbed or not in real time and adjusts the controller parameters to ensure the stability and accuracy of the system.

5. The real-time dispatching-control cascade system of double cranes as claimed in claim 3, wherein said control layer further comprises a fault tolerance module, the input end of which is connected to the crane, and the output end of which is connected to said controller, for detecting whether the crane is in fault in real time and controlling said controller to avoid the collision of double cranes.

6. The real-time dispatch-control cascade system of twin cranes of claim 5, wherein the fault tolerant module further comprises a fault tolerant controller and a fault detector in series; the input end of the fault detector is connected with the crane, and whether the crane has a fault or not is detected in real time; the output end of the fault-tolerant controller is connected with the controller, and if the fault detector does not detect the crane fault, the fault-tolerant controller does not work; if the fault detector detects a crane fault, the fault-tolerant controller adjusts the output of the controller to prevent double-crane conflict caused by the fault.

7. The real-time scheduling-controlling cascade system of a twin crane as set forth in claim 3, wherein a laser range finder is further provided on said position sensor; the main motor of the crane is also provided with an encoder; and the laser range finder and the encoder are used for jointly detecting and feeding back real-time position information of the crane.

8. A real-time scheduling-control cascading method of double cranes is characterized by comprising the following steps:

step 1: receiving task information required to be scheduled by the double cranes according to the scheduling layer, and performing recombination scheduling and real-time optimization on the task information to generate a scheduling plan of the double cranes;

step 2: transmitting the scheduling plan to a control layer for real-time regulation and control calculation, and outputting a real-time manipulated variable;

and step 3: and transmitting the real-time manipulated variable to a main motor of the crane for calculation to generate moment information corresponding to the real-time manipulated variable, and driving the crane to move in real time by the main motor of the crane according to the moment information.

9. The tandem scheduling-control method of real-time scheduling of twin cranes of claim 8 wherein the regrouping scheduling and real-time optimization further comprises the steps of:

step 1.1: transmitting the task information received by the task receiving module to the detection module, and detecting whether the task information responds to the dynamic task;

step 1.2: if the task information has no dynamic task response, transmitting the task information without the dynamic task response to the optimization module; if the task information has dynamic task response, transmitting the task information with dynamic task response to a recombination module, and performing recombination scheduling to generate recombined task information;

step 1.3: and transmitting the task information without the dynamic task response/the recombined task information to the optimization module for real-time optimization to generate a scheduling plan.

10. The method of real-time dispatch-control cascade of twin cranes of claim 9 wherein the real-time regulatory calculations further comprise the steps of:

step 2.1: the position sensor monitors and feeds back real-time position information of the crane in real time;

step 2.2: transmitting the dispatching plan to the selection module for selection processing, and selecting an optimal set value;

step 2.3: transmitting the real-time position information and the optimal set value to the selection module, and performing deviation calculation to generate an optimal control value;

step 2.4: and inputting the optimal control value into a controller for control, and outputting a real-time manipulated variable.

Technical Field

The invention relates to the field of automatic container terminal yard crane scheduling, in particular to a real-time scheduling-control cascade system and a real-time scheduling-control cascade method for double cranes.

Background

Automated container terminal yards are typically comprised of several bays, each bay being equipped with one or more cranes for loading and unloading containers. The wharf mainly comprises three operation flows of an inlet box, an outlet box and a transfer box. At present, due to the fact that the operation flexibility of the double-crane configuration is high, most of containers entering and leaving the container area adopt a mixed stockpiling mode, and the operation efficiency of a yard is improved.

At present, the inlet and outlet boxes of an automatic container terminal storage yard are mixed and stored and are dispersed on the corresponding shellfish position and the arrangement position of a box area. Two automatic yard cranes (sea side crane and land side crane) configured in a box area run on the same rail, the sea side crane is mainly responsible for the operation related to the ship unloading process, the land side crane is mainly responsible for the operation related to the outer container truck, the two cranes cooperatively operate in a relay mode, and if one crane stops due to a fault, the other crane can take over the operation. Two ends of the box area are respectively provided with a cross-over area, each cross-over area is provided with a plurality of cross-over positions, and containers enter and exit the storage yard at the cross-over positions.

The real-time and efficient crane scheduling plan is the premise of wharf operation optimization. At present, a wharf manager usually makes a dispatching plan of a crane in a static mode, but the timeliness of the operation mode is poor, and if the operation is interrupted or a new task arrives, the optimality of a given dispatching scheme is broken, and the execution efficiency is reduced.

The accurate and stable control scheme is the guarantee of the normal operation of the crane. Because the two cranes work on the same track, interference is inevitably generated, and if the interference is not processed in time, conflict is generated, so that operation interruption is caused, and the overall performance of the automatic wharf is influenced. Therefore, avoiding the conflict of the double cranes is a necessary condition for the normal and orderly operation of the cranes. For each scheduled task execution, the set point of the control system is determined by the target position of the task, the goal of the control being that the output value of the system quickly follows the desired set point under disturbance (disturbance) conditions. However, the set value of the existing control system is given in an off-line state, and is not optimal, if disturbance occurs, the steady-state error is large, and conflicts are easy to occur among cranes due to disturbance avoidance failure.

In conclusion, the existing scheduling plan has no real-time performance and low scheduling efficiency; the set value of the control system in the control scheme has no optimality, and the accuracy and the stability of the system output are poor. In addition, the scheduling plan and the control scheme are mutually separated and independent and do not have the functions of feedback and regulation. When a fault occurs, a corresponding fault-tolerant scheme is not considered, so that the operation is not sustainable, and the overall performance of the automatic wharf is influenced.

Disclosure of Invention

The invention aims to provide a real-time scheduling-control cascading system and a real-time scheduling-control cascading method for double cranes. The system and the method aim to solve the problems of poor real-time performance and low efficiency of a dispatching plan and poor accuracy and stability of a control system, realize parameter sharing and mutual feedback coordination of the dispatching plan and a control scheme, and ensure that the system keeps the stability and the accuracy of continuous operation when a fault occurs.

In order to achieve the above object, the present invention provides a real-time scheduling-control cascade system of a dual crane, comprising:

the scheduling layer receives task information scheduled by the double cranes, performs recombination scheduling and real-time optimization, and obtains a scheduling plan;

and the input end of the control layer is connected with the dispatching hierarchy connection structure, the output end of the control layer is connected with a main motor of the crane, calculation is carried out according to a dispatching plan, an optimal control value is generated, and the crane is regulated and controlled in real time according to the optimal control value.

Most preferably, the scheduling layer comprises a task receiving module, a detection module, a recombination module and an optimization module; the task receiving module receives task information needing to be scheduled by the double cranes; the input end of the detection module is connected with the task receiving module and used for detecting whether the task information responds to the dynamic task; the input end of the recombination module is connected with the first output end of the detection module, and task information after responding to the dynamic task is recombined and scheduled; the first input end of the optimization module is connected with the output end of the recombination module, the second input end of the optimization module is connected with the second output end of the detection module, the output end of the optimization module is connected with the control layer, and task information which completes recombination scheduling after no response dynamic task/response dynamic task is optimized in real time.

Most preferably, the control layer comprises a selection module, a position sensor and a controller; the input end of the position sensor is connected with the crane, and the real-time position information of the crane is monitored in real time; the first input end of the selection module is connected with the cascade structure of the optimization module, the second input end of the selection module is connected with the position sensor, the scheduling plan is selected, the optimal set value is selected, deviation calculation is carried out according to the optimal set value and real-time position information, and the optimal control value is generated; the input end of the controller is connected with the selection module, the output end of the controller is connected with a main motor of the crane, the controller is controlled according to the optimal control value, and real-time manipulated variables are output; the main motor of the crane is connected with the crane, and the crane is driven to move in real time according to the real-time manipulated variable; the selection module, the controller, the main motor of the crane, the crane and the position sensor are sequentially connected to form a closed loop negative feedback loop.

Most preferably, the control layer further comprises a self-adaptive controller, wherein the input end of the self-adaptive controller is connected with the position sensor, the output end of the self-adaptive controller is connected with the controller, whether the crane is disturbed or not is monitored in real time, and the parameters of the controller are adjusted, so that the stability and the accuracy of the system are guaranteed.

Most preferably, the control layer further comprises a fault tolerance module, wherein the input end of the fault tolerance module is connected with the crane, the output end of the fault tolerance module is connected with the controller, whether the position sensor has a fault or not is detected in real time, the controller is regulated and controlled, and the conflict between the two cranes is avoided.

Most preferably, the fault tolerant module further comprises a fault tolerant controller and a fault detector connected in series; the input end of the fault detector is connected with the crane to detect whether the crane has a fault in real time; the output end of the fault-tolerant controller is connected with the controller, and if the fault detector does not detect the crane fault, the fault-tolerant controller does not work; if the fault detector detects a crane fault, the fault-tolerant controller adjusts the output of the controller to prevent the double-crane conflict caused by the fault.

Most preferably, the position sensor is also provided with a laser range finder; the main motor of the crane is also provided with an encoder; and the real-time position information of the crane is detected and fed back through the laser range finder and the encoder together.

The invention also provides a real-time scheduling-control cascading method of the double cranes, which comprises the following steps:

step 1: receiving task information required to be scheduled by the double cranes according to the scheduling layer, and performing recombination scheduling and real-time optimization on the task information to generate a scheduling plan of the double cranes;

step 2: transmitting the scheduling plan to a control layer for real-time regulation and control calculation, and outputting a real-time manipulated variable;

and step 3: and transmitting the real-time manipulated variable to a main motor of the crane for calculation to generate moment information corresponding to the real-time manipulated variable, and driving the crane to move in real time by the main motor of the crane according to the moment information.

Most preferably, the reassembly schedule and real-time optimization further comprises the steps of:

step 1.1: transmitting the task information received by the task receiving module to a detection module, and detecting whether the task information responds to the dynamic task;

step 1.2: if the task information has no dynamic task response, transmitting the task information without the dynamic task response to the optimization module; if the task information has dynamic task response, transmitting the task information with the dynamic task response to a recombination module, and performing recombination scheduling to generate recombined task information;

step 1.3: and transmitting the task information/recombined task information without dynamic task response to an optimization module, and performing real-time optimization to generate a scheduling plan.

Most preferably, the real-time regulation calculation further comprises the following steps:

step 2.1: the position sensor monitors and feeds back real-time position information of the crane in real time;

step 2.2: transmitting the scheduling plan to a selection module for selection processing, and selecting an optimal set value;

step 2.3: transmitting the real-time position information and the optimal set value to a selection module, and performing deviation calculation to generate an optimal control value;

step 2.4: and inputting the optimal control value into a controller for control, and outputting a real-time manipulated variable.

By applying the method, the problems of poor real-time performance and low efficiency of the scheduling plan and poor accuracy and stability of the control system are solved, the parameter sharing and mutual feedback coordination of the scheduling plan and the control scheme are realized, and the stability and the accuracy of continuous operation of the system are ensured when a fault occurs.

Compared with the prior art, the invention has the following beneficial effects:

1. the system realizes the allocation, the scheduling and the control of the crane through a scheduling-control cascade structure, has simple and precise logic structure and is easy to realize.

2. In the system scheduling-control cascade structure, parameters of a scheduling layer and a control layer are shared and coordinated with each other, and the scheduling plan of the crane is formulated, executed and fed back together.

3. The system scheduling layer can detect that the task information has temporary task insertion or initial task change, and completes task information recombination scheduling;

4. the system adopts a fault tolerance and self-adaptive control scheme, and in order to prevent the controller from misjudging to cause conflict caused by the fault of the crane, the self-adaptive controller corrects the parameters of the controller after the control system is disturbed, thereby maintaining the stability and the accuracy of the control system.

Drawings

FIG. 1 is a layout diagram of a dual-crane dispatching layout in a box area of an automated wharf storage yard provided by the present invention;

FIG. 2 is a schematic diagram of a real-time scheduling-control cascade system according to the present invention;

FIG. 3 is a flow chart of the laser range finder for detecting real-time position information of a crane provided by the invention;

FIG. 4 is a flow chart of encoder fault detection provided by the present invention;

fig. 5 is a schematic flow chart of a real-time scheduling-control cascading method provided by the present invention.

Detailed Description

The invention will be further described by the following specific examples in conjunction with the drawings, which are provided for illustration only and are not intended to limit the scope of the invention.

As shown in FIG. 1, the layout of the box area of the automated wharf storage yard is that the sea-side crane and the land-side crane span the box area, run on the same track and cannot span. The method comprises two types of tasks, namely a box storing task and a box taking task, and comprises the following operation processes: 1) when the container storage operation is executed, the container is lifted by the crane from the two end cross-connecting positions and is conveyed to the corresponding container storage positions; 2) when the container taking operation is executed, the container is lifted from the container taking position by the crane and is conveyed to the corresponding delivery positions at the two ends.

In order to shorten the reciprocating travel distance of a single crane and improve the system operation efficiency of the loading and unloading ship in the peak period, a relay operation mode is adopted. A buffer area is arranged at a certain position in the middle of the box area, and after a container is lifted from the transfer area by one crane, the container is transferred to the buffer area; then another crane takes over the container in the buffer area and transports the container to the target position to complete relay operation.

The invention relates to a real-time scheduling-control cascade system of a double crane, which comprises a scheduling layer and a control layer which are connected in a cascade structure, as shown in figure 2; the scheduling layer receives task information scheduled by the double cranes, and performs recombination scheduling and real-time optimization to obtain a scheduling plan; the output end of the control layer is connected with a main motor 7 of the crane, calculation is carried out according to a scheduling plan, an optimal control value is generated, and the crane 8 is regulated and controlled in real time according to the optimal control value.

The scheduling layer comprises a task receiving module 1, a detection module 2, a recombination module 3 and an optimization module 4; the task receiving module 1 receives task information needing to be scheduled by the double cranes; the input end of the detection module 2 is connected with the task receiving module 1, and whether the task information responds to the dynamic task is detected; the input end of the recombination module 3 is connected with the first output end of the detection module 2, and task information after responding to the dynamic task is recombined and scheduled; the first input end of the optimization module 4 is connected with the output end of the recombination module 3, the second input end of the optimization module is connected with the second output end of the detection module 2, and the output end of the optimization module is connected with the control layer, so that task information which completes recombination scheduling after no response dynamic task/response dynamic task is optimized in real time; the real-time optimization is to shorten the dead time of the crane, improve the response efficiency of dynamic tasks, minimize the task completion time and improve the operation efficiency of the automatic wharf.

The standard for detecting whether the task information responds to the dynamic task in the detection module 2 is to judge whether the task information has temporary task insertion or initial task change in the period; if the temporary task insertion or the initial task change in the period exists, responding to the dynamic task; and if the temporary task insertion or the initial task change in the period does not exist, the dynamic task is not responded.

In the same scheduling period, in order to facilitate the turnover of the crane 8, the making period of the scheduling plan should be longer than the average duration of the first task of the operation of the crane 8, so that the crane 8 executing the task is in a rescheduleable state during the next scheduling.

The control layer comprises a selection module 5, a position sensor 9, a controller 6, a self-adaptive controller 10 and a fault tolerance module; the input end of the position sensor 9 is connected with the crane 8, and the real-time position information of the crane 8 is monitored in real time; the first input end of the selection module 5 is connected with the cascade structure of the optimization module 4, the second input end of the selection module is connected with the position sensor 9, the scheduling plan is selected, the optimal set value is selected, deviation calculation is carried out according to the optimal set value and real-time position information, and the optimal control value is generated; the input end of the controller 6 is connected with the selection module 5, the output end of the controller is connected with a main motor 7 of the crane, the controller controls the crane according to the optimal control value and outputs a real-time manipulated variable; the main motor 7 of the crane is connected with the crane 8, and corresponding torque information is generated according to the real-time manipulated variable to drive the crane 8 to move in real time; the selection module 5, the controller 6, the main motor 7 of the crane, the crane 8 and the position sensor 9 are connected in sequence to form a closed loop negative feedback loop.

The input end of the self-adaptive controller 10 is connected with the position sensor 9, the output end of the self-adaptive controller is connected with the controller 6, whether the crane 8 generates disturbance or not and the parameter of the controller 6 drifts or not are monitored in real time, the parameter of the controller 6 is adjusted on line according to the type and the degree of the disturbance, and the stability and the accuracy of the system are guaranteed; the corrected controller 6 outputs an accurate command to a main motor 7 of the crane to determine a safe running track of the crane 8.

The input end of the fault tolerance module is connected with the crane 8, the output end of the fault tolerance module is connected with the controller 6, whether the crane 8 breaks down or not is detected in real time, the controller 6 is regulated and controlled, and the double cranes are prevented from colliding.

The fault tolerance module further comprises a fault tolerance controller 12 and a fault detector 11 which are connected in series; the input end of the fault detector 11 is connected with the crane 8, and whether the crane 8 breaks down or not is detected in real time; the output end of the fault-tolerant controller 12 is connected with the controller 6, and if the fault detector 11 does not detect the fault of the crane 8, the fault-tolerant controller 12 does not work; if the fault detector 11 detects a fault in the crane 8, the fault-tolerant controller 12 adjusts the output of the controller 6 to prevent the fault from causing a double-crane conflict.

The impact of the crane 8 fault on the control system is large, which leads to the misjudgment of the controller 6 and the output of results with poor quality and even opposite quality, thus leading to serious accidents such as collision of the crane 8. If the fault occurs, before the fault is not solved, the control parameters are corrected by the fault-tolerant controller 12 so as to prevent the control of the crane 8 from generating serious deviation to cause the occurrence of accidents.

The position sensor 9 is also provided with a laser range finder; the main motor 7 of the crane is also provided with an encoder; the real-time position information of the crane 8 is detected and fed back through the laser range finder and the encoder together.

As shown in fig. 3, there are two groups of laser range finders, each of which is a laser range finder a and a laser range finder B, respectively disposed on two sides of two cranes 8, and the real-time position information L of the crane 8 is obtained by detecting the position of the crane 8 at each time in a redundant manner and taking the average value of the positions of the data_AB(ii) a The encoder is a rotary encoder for calculating the real time of the crane 8Position L_C(ii) a Real-time position information L of crane 8 detected by laser range finder_ABAnd the real-time position L of the crane 8 calculated by the rotary encoder_CComparing the difference, and receiving the real-time position information L detected by the laser range finder when the difference result is within the allowable error range P_ABThe distance measurement is effective, and the crane 8 normally runs; when the difference between the two results exceeds the allowable error range P, it is necessary to check whether the laser range finder has a fault.

As shown in fig. 4, a fixed position positioning mode is adopted to check whether the rotary encoder works normally, limit switches are arranged at the sea side, the land side and the sea-land boundary position, and when the encoder passes through the three positions, the limit switches are triggered to enable the encoder to measure data at the positions: comparing the data e, the data f and the data g with the actual position, and if more than one data exceeds the allowable error range, judging that the encoder has a fault; otherwise, the encoder is normal and the operation continues.

The invention also provides a real-time scheduling-control cascading method of the double cranes, which comprises the following steps as shown in figure 5:

step 1: receiving task information required to be scheduled by the double cranes according to the scheduling layer, and performing recombination scheduling and real-time optimization on the task information to generate a scheduling plan of the double cranes; the reassembly scheduling and real-time optimization further comprises the steps of:

step 1.1: transmitting the task information received by the task receiving module 1 to the detection module 2, and detecting whether the task information responds to the dynamic task;

step 1.2: if the task information has no dynamic task response, transmitting the task information without dynamic task response to the optimization module 4; if the task information has dynamic task response, transmitting the task information with dynamic task response to the recombination module 3, and performing recombination scheduling to generate recombined task information;

step 1.3: and transmitting the task information/recombined task information without dynamic task response to the optimization module 4 for real-time optimization to generate a scheduling plan.

Step 2: transmitting the scheduling plan to a control layer for real-time regulation and control calculation, and outputting a real-time manipulated variable; the real-time regulation and control calculation further comprises the following steps:

step 2.1: the position sensor 9 monitors and feeds back real-time position information of the crane 8 in real time;

step 2.2: transmitting the dispatching plan to a selection module 5 for selection processing, and selecting an optimal set value;

step 2.3: transmitting the real-time position information and the optimal set value to a selection module 5, and performing deviation calculation to generate an optimal control value;

step 2.4: and inputting the optimal control value into a controller for control, and outputting a real-time manipulated variable. And step 3: and transmitting the real-time manipulated variable to a main motor 7 of the crane for calculation to generate moment information corresponding to the real-time manipulated variable, and driving the crane 8 to move in real time by the main motor 7 of the crane according to the moment information corresponding to the real-time manipulated variable.

The working principle of the invention is as follows:

receiving task information required to be scheduled by the double cranes according to the scheduling layer, and performing recombination scheduling and real-time optimization on the task information to generate a scheduling plan of the double cranes; transmitting the scheduling plan to a control layer for real-time regulation and control calculation, and outputting a real-time manipulated variable; and transmitting the real-time manipulated variable to a main motor of the crane for calculation to generate moment information corresponding to the real-time manipulated variable, and driving the crane to move in real time by the main motor of the crane according to the moment information.

In conclusion, the invention solves the problems of poor real-time performance and low efficiency of the dispatching plan and poor accuracy and stability of the control system, realizes parameter sharing and mutual feedback coordination of the dispatching plan and the control scheme, and ensures that the system keeps the stability and the accuracy of continuous operation when a fault occurs.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.