A novel stage hydraulic monitoring system based on Internet of Things (IoT) is proposed in this paper. Compared with the traditional wired system, the proposed system is a flexible working method and can save the cost. Furthermore, it has the low power consumption, high safety, and large scale network. The real-time pressure and flow data can be collected by using the nodes in ZigBee network. The fault detection and diagnosis process was used in this study, which was facilitated by measuring pressure of flow. When the monitored data exceeds the normal range, some failure may occur in the stage hydraulic system. If any failure occurs in the circuit, the maintainers can be informed immediately, which can greatly improve maintenance efficiency, ensuring the failure to be eliminated in time. Meanwhile, we can take advantage of wireless sensor network (WSN) to connect the multiple loops and then monitor the loops by using ZigBee technology, which greatly improves the efficiency of monitoring.
It is well known that the lifting platform is the indispensable part in a theatre. It has many important functions, such as changing the set rapidly, meeting the process arrangement of the stage, making special atmosphere and effect, and changing the stage form according to the needs of performance. Chen and Wang studied the hydraulic control system design of the test platform, and the hydraulic control system of cutter disk/segment erector/screw conveyer loading simulation and driving experimental unit, simulation of thrust control system unit, and motion control test system of hydraulic cylinder in multi-DOF segment erector unit were discussed separately [
Because the stage of the hydraulic system is relatively large, the failure is unavoidable. The causes of the failure are varied, such as stained aging of hydraulic components, all kinds of interference of impurity, oil corrosion, and instability of flow and pressure of the hydraulic loop. Once there is a failure in the stage hydraulic system, it is difficult to accurately lock the location of the failure and find out the reasons of the failure. It is also very difficult to detect the fault of the hydraulic components, which will result in low work efficiency, affecting the speed of the maintenance, and even it is likely to affect the performance of the whole system. Therefore, it is very necessary to design an effective stage hydraulic safety monitoring system so as to locate the position of the failure in time and then take measures to cut losses to a minimum.
IoT is an interconnected network, in which the objects can transfer data over the network. It is through radio frequency identification (RFID), sensors, global positioning systems, and other information sensing devices to connect anything in the world with the Internet and conduct information exchange and communication between the object and network according to the agreed protocol. In [
Compared with other IoT technology, ZigBee has a number of advantages, for example, low power consumption, high safety performance, the maximum network size and low cost. In addition, ZigBee wireless network also has a low complexity and data rate. These features make ZigBee suitable for automatic control and remote control and can be embedded in a variety of devices. In addition to a stable two-way and multipoint communications capability, ZigBee technology also has a flexible adaptability and scalability, and therefore it does not require complex server and other equipment. Full function device and simplified function device are the only part of any ZigBee network. The network can be expanded by increasing the full function device or simplified function device, which provides great flexibility for a variety of applications. Yi et al. have thoroughly evaluated ZigBee performance under WiFi interference for smart grid applications. A theoretical model has been introduced, followed by a corresponding simulation model, which completely reflects the ZigBee and WiFi coexistence features via MATLAB or Simulink in [
According to the above advantages of ZigBee technology, we choose ZigBee to build a wireless network for data communication. Traditional method for monitoring the stage can be only performed in one loop, and when the other circuit fails, the monitoring system cannot find the fault in time. Using ZigBee technology can take advantage of WSN to connect multiple loops and then monitor multiple loops, greatly improving the efficiency of monitoring. By using the nodes in ZigBee network, we can collect real-time pressure and flow data. With establishing and running the stage network monitoring system, the stage management department can achieve the real-time operating status. When a fault occurs in one loop, the nearest maintenance personnel can be immediately informed. So it can greatly improve the response speed of stage operation failure, ensuring the failure excluded in time, and personnel can receive timely rescue, in order to protect the safe operation of the stage. By analyzing and counting stage log data, we can know the type and probability of the failure during the operation of stage. It helps to analyze the potential insecurity, provide direct data to support routine maintenance, improve the pertinence of maintenance work, and reduce maintenance costs.
This paper is organized as follows. In Section
ZigBee network has three topology forms, namely, star topology, tree topology, and mesh topology [
The system consists of three parts, that is, sensor node part, coordinator part, and PC part. It consists of a fully functional coordinator, multiple end nodes equipped with pressure, and flow sensor to achieve point to point transmission. Coordinator is connected with the PC via the serial port, and end nodes are arranged in different locations of environmental monitoring area to monitor environmental parameters through sensors on it. Finally, the monitored data of the stage hydraulic system is sent to the coordinator through the antenna in wireless method. Due to the connection between coordinator and PC, environmental monitoring results can be presented on the PC, realizing monitoring of pressure and flow of the node. The diagram of stage hydraulic system is shown in Figure
The diagram of stage hydraulic system.
The main task of this system is to monitor the pressure and flow of the stage. When the particular node index is higher than the threshold value, the monitoring system will emit an alarm to the staff. The PC receives and processes the data and then draws real-time dynamic curves, while the host computer can save the measured data of all nodes up to facilitate postviewing.
Software design of the system is carried out in C language based on the Z-Stack protocol stack [
During the experiment, let each node (including the coordinator and a plurality of end devices) download IAR program via an emulator which has been compiled. As the download completed, reset the node and install the antenna, and then reboot the node, so the node can start working.
The sensor part consists of pressure sensor and flow sensor. When the stage hydraulic system works, the two sensors work as well. We can connect the sensors with one IO port of CC2530 chip via data line. When oil flows through pressure sensor and flow sensor, the real-time data can be transmitted to CC2530 chip. The measured data is analog signal and can be converted into digital signal by the AD conversion section in CC2530, thus continuing subsequent data transmission. In this paper, we select IO port P07 as the access point.
The coordinator is the core part of the stage hydraulic monitoring system. Its role is to establish the network and open the allowed binding function after power on. The sensor nodes join the network after power on and initiate binding request automatically. After the binding between sensor nodes and coordinator, the converted digital signal is transmitted to the coordinator in wireless transmission method. At last, the measured data are transmitted to the PC via serial connection and then conduct the data processing. Figure
Model of the wireless sensor nodes.
Workflow of the ZigBee network.
Each ZigBee network has one and only one core part to build a ZigBee network. The network architecture diagram is shown in Figure
Network architecture diagram.
The flow chart of the coordinator.
The coordinator plays a very important role in building up the entire network, binding with the sensor nodes to receive data, and transmitting the received data via the serial port to the connected PC.
According to the function requirements of the coordinator node, a SampleApp task is defined in the application layer of the node to complete data collection and communication in the user layer. User tasks are defined as the serial communication events, wireless communication events, and sleep events. Serial communication events are mainly for data communication with the host computer; wireless communication events are mainly mutual communication between the nodes, including flow and pressure data acquisition [
Communication between the coordinator node and each sensor node is in a single-point transmission method; end devices communicate only with the coordinator. For the realization of this function, the coordinator must know the network address of each collection node, which requires each node to send its network address to the coordinator after joining in the network. After receiving the network addresses, the coordinator establishes a network address table to store these addresses, so that the user collects data based on the address table for each sensor, providing convenient communication between the coordinator node and each sensor node.
Firstly, the coordinator node needs to complete the initialization of serial port, network operating system, and such procedures. There are mainly the initialization of the operating system, the serial port, and the hardware. The initialization is performed with functions osal_init_system ( ), MT_UartInit ( ), and HAL_BOARD
Since the Z-Stack protocol stack has provided the framework of agreement, the coordinator’s code in IAR EW8051 only needs to be modified in the App layer. The ZigBee network follows the beacon-enabled mode, in which communications are synchronized by specific frames (beacons) which are periodically emitted by the coordinator. For distributing the beacon interval of a ZigBee cluster tree among the superframes of the clusters, the algorithm follows the time division policy. In order to avoid those periods without any activity in any cluster, the goal is to maximize the use of the beacon interval of the network. So the assignment of the superframe orders should be considered.
In ZigBee sensor networks, the data are forwarded from the end nodes to a gateway or central node which most probably will reside in the coordinator. This centralization may cause the coordinator to become a traffic bottleneck. To avoid this situation, the active time of the coordinator should be privileged. A simple algorithm that prioritizes the role of the coordinator is to design its superframe order (SOl) with twice the value of that of the rest of the cluster coordinators:
As
Using these values and solving (
In order to operate as a coordinator in a beacon-enabled cluster network, a node has to transmit beacons and receive the contention access period for communicating with the nodes associated with it. In addition, a coordinator maintains synchronization with its parent by receiving beacons from it. The activity of a coordinator depends significantly on its location in the network and hence the requested throughput. As the power consumption of radio transmission and reception modes is quite similar, we estimate that the power consumption of a coordinator during contention access period equals the reception mode power consumption. The data flow to the uplink direction is performed by long MAC payloads containing sensing items per each frame. The duty cycle of a coordinator (DCCOOR) is modeled as follows:
Similarly, the average power consumption of a coordinator can be calculated as follows:
The average coordinator power consumption is a function of the uplink data transmission interval. As in the case of the device power consumption analysis, the network scanning interval equals 3 hours. With very low data rate network, coordinator power consumption can go below 200
The program of the end device is almost the same with the coordinator. There will be a little difference in a few key points, such as the selection of the equipment type. The type of the collector node is the coordinator, while the sensor node is only served as an end device node to start. The flow chart of end device is shown in Figure
The flow chart of end device.
As mentioned above, the entire network can support more than 64000 ZigBee nodes ideally. Multiple ends are utilized in the experiment, and we only need to download the “Coordinator” program, respectively, to these ends. All the PAN ID of the end nodes is the same as the coordinator, which will be automatically connected to the same ZigBee network.
When the establishment of the network is complete, end nodes can be open to join the network. Finish the initialization of the operating system of a node and the serial port, and then join the network through sending the request and calling the corresponding function. Finally, the sensor nodes also need to be bound to the coordinator node.
The first step is to initialize the operating system of each sensor node, LCD, and UART serial port. osal_init_system ( ), InitLcd ( ), HalUARTInit ( ), and other functions are needed to conduct the initialization. Secondly, when there is a network, the network layer will give sensor nodes feedback information of the ZDO layer. Requesting to join the network through the network layer and the function NLME_NetworkFormationRequest ( ) is required to join the network. Thirdly, the binding of the sensor nodes and coordinator node is necessary. After receiving the response of joining the network, the sensor nodes call ZDP_EndDeviceBindReq ( ) function to request binding. After the binding, sending and receiving data can be realized. The fourth step is sending the data. We need to register the event, set the number, and send time. The function SampleApp_TaskID is for registration event, function SAMPLEAPP_AA_PERIODIC_MSG_EVT is for setting number, and function SAMPLEAPP_SEND_PERIODIC_MSG_TIMEOUT is used to set time for periodic sending data. When a registered event occurs, SampleApp_SendPeriodicMessage ( ) is required to set the transmitted information.
To be able to operate in a ZigBee network, an end device receives beacons and exchanges data with a coordinator. If a communication link to the coordinator is lost an end device performs a network scanning. The rest of the time a device is in the sleep mode. The duty cycle of a device (DCDEV) is calculated with beacon receptions, uplink and downlink data exchanges, and network scanning. The average network scanning interval (INS) depends on device speed and radio link quality. DCDEV can be computed as follows:
Similarly, the device power consumption is expressed as follows:
The average end device power consumption is a function of the uplink data transmission interval. The network scanning interval is approximated to be averagely 3 hours, which corresponds to a deployment with low dynamics and good link qualities. In general, the power consumption decreases with longer beacon and uplink data transmission intervals, since the energy required for beacon receptions and data transmissions diminishes. At the longer beacon intervals, the network scanning power becomes significant, since the network scanning energy increases directly the beacon interval.
As for the PC part, the serial debugging assistant can be used to view data. The serial port, baud rate, parity bit, data bit, and stop bit have to be set up when using them. The received data can be displayed in the data box after opening the serial port. In order to strengthen the functions of the monitoring system and intuitively display the operating statue of the monitoring system, we design a stage hydraulic monitoring system based on MATLAB GUI interface. The interface of stage hydraulic monitoring system includes real-time display of the received data, real-time data curve drawing, selection of COM port, selection of baud rate, selection of data bits and stop bits, definition of data read interval, open serial, off serial, and other functions.
To obtain the monitoring data, the serial port, baud rate, parity bit, data bit, and stop bit need to be set up. If the serial port is open, the received data can be displayed in the data box of the serial debugging assistant. All the parameters of serial port in MATLAB GUI interface are set up as well. Details of the test data are as follows: Alert data: {32 32 49 46 48 86 32 32 49 46 48 86 32 32 49 46 48 86}. Normal data 1: {80 82 69 83 85 82 69 58 56 53 32 32 10 70 76 79 87 58 56 53 10 77} (received byte = 330). Normal data 2: {84 69 77 80 49 58 50 56 32 67 10 71 65 78 58 50 56 32 67 10} (received byte = 2200). Real-time data can be displayed, and real-time curve can be plotted according to these data. Figure
GUI monitoring interface under normal circumstances.
An alarm module is also designed in the PC software monitoring system. When the monitored data exceeds the normal range as Figure
GUI alarm interface when pressure or flow exceeds normal.
Compared with traditional wired system, the proposed structure not only has a flexible working way, but also saves space and costs and is easy to implement. We can conduct real-time monitoring of pressure and flow data. If any failure occurs in the circuit, the maintenance personnel can be informed immediately, which can greatly improve maintenance efficiency and ensure the failure to be eliminated in time and success of the performance.
With the help of ZigBee technology, the proposed system can carry out real-time monitoring of the stage hydraulic system and successfully achieve data collection and real-time display of dynamic curve. A MATLAB GUI interface is designed to intuitively display the operating statue of the monitoring system. Once a failure occurs, the alarm will be triggered to inform the maintainers to find the location of the failure in time. Therefore, this system can improve maintenance efficiency and ensure the safety of the performers and the success of the performance.
The authors declare that they have no conflict of interests.
This study is supported by the National Science-Technology Support Plan Projects (no. 2012BAH38F01-04).