1 Introduction
With the improvement of people's cultural life, the requirements for the quality of stage performances are getting higher and higher. The modernization and intelligentization of stages are inevitable development trends. Although some stages in China have referenced foreign stage forms, their overall technical level is relatively low and cannot meet the various functional requirements of stage use. Addressing the current situation where theater (including television studio) stages have fixed platforms, monotonous shapes and styles, and the overall stage design fails to meet performance requirements, this paper, based on the overall process design during stage construction, utilizes PLC control and electromechanical-hydraulic integration technology to enable the communication system to achieve good and fast communication between the host computer, PLC, and on-site intelligent instruments, thereby completing the real-time display and control of on-site data. It realizes the stage's lifting, moving lifting, rotating, lifting and rotating, extending, and extending and lifting movements, thus achieving coordinated changes between the stage, stage design, actors, scenery, and lighting, making the performances more colorful, diverse, and ever-changing. Once a smart stage is built with a single investment, its various combination and transformation forms can meet the requirements of various performance programs. Therefore, it can eliminate many of the drawbacks of repeatedly building different performance stages for different performances. In addition, it increases the variety of performance scenes and enriches the performance effect.
This article takes the design, installation and debugging of the intelligent stage in the 800m² studio of a certain broadcasting and television center as the research background to illustrate the application of S7-200[1] in the stage platform control.
2. Composition of the Intelligent Stage Control System
2.1 Stage Platform Composition
The stage platform can achieve various movements such as lifting, moving, rotating, lifting and rotating, extending and retracting, and extending and lifting. The basic changes of the stage can reach dozens to nearly a hundred, thereby achieving the function of coordinated changes between the stage, stage design, actors, scenes, and lighting. This avoids the waste of manpower, material resources, and financial resources caused by repeatedly building a basic stage for one-time use in the past, shortens the stage preparation cycle for programs, and makes wonderful performances more colorful and ever-changing.
The intelligent stage platform control system primarily controls the movement of individual stage platforms. Figure 1 shows the intelligent stage platform structure of an 800m² studio in a broadcasting and television center, comprising five lifting platforms, one aisle platform, one rotating platform, and one T-shaped platform. Platforms 1-5 are lifting platforms, platform 6 is the aisle platform, platform 7 is the rotating platform, and platform 8 is the T-shaped platform with telescopic functionality. All eight moving platforms have selectable manual and automatic operating modes. When the selected mode is used, all actions are performed by a PLC. Monitoring and control of the entire moving stage platform can be achieved via a host computer.
Figure 1. Stage platform composition
2.2 Table Motion Control Principle
Taking the lifting platform control system as an example, the working principle of the lifting platform control circuit is explained [2]. As shown in Figure 2, the stage platform movement part consists of a unit stage platform, fork arm lifting and hydraulic transmission structure; while the platform monitoring part consists of a host monitoring computer and a PLC; the pump station provides the hydraulic power source. When the system starts, the host computer issues the instruction for the stage platform movement amount, the PLC receives the instruction, makes a judgment and decision, and then issues commands to the pump station current and hydraulic transmission mechanism. The pump station starts working, and the oil cylinder piston in the hydraulic transmission mechanism pushes the fork arm mechanism to drive the lifting stage to move up and down according to the input requirements. At this time, the encoder installed on the fork arm moving roller starts to rotate and record the stroke, and it detects the lifting height of the lifting platform at any time. The system uses a KSJ1200 encoder with a rotation speed of 0.8 revolutions/second. The encoder rotates about 5 revolutions in the entire 1200mm stroke, generating 500 pulses per revolution, generating a total of 5×500=2500 pulses. On average, 1 pulse represents 1200/2500=0.5mm. In this way, the control accuracy can be controlled within ±1mm. Each lifting stage can operate independently or synchronously. Stages of various sizes, shapes, areas, and functions can be combined according to their different requirements. Similarly, the working principle of the telescopic stage control system is roughly the same.
Figure 2. Schematic diagram of the control circuit for the lifting platform.
By adjusting the height, extension, or rotation of each stage unit, the requirements for overall stage changes, as well as the height adjustment or rotation of various props and personnel, can be met during the performance.
2.3 Configuration of Tabletop Motion Control System
As shown in Figure 3, the stage platform control system mainly consists of four parts: the control panel, the PLC control cabinet, the hydraulic transmission mechanism, and the stage platforms for each moving unit.
Figure 3 Schematic diagram of the table motion control system
(1) Control panel
The control panel primarily handles system operations. The touchscreen and industrial computer operate independently. System operations, specifically various actions on the unit stage, can be performed via the touchscreen interface, while system programming can be completed through the IPC programming interface.
(2) ADAM4520
The Adam block serves as a communication interface, converting the communication protocol between the host computer and the PLC into the RS-422/RS-485 serial communication protocol standard, thus enabling communication.
(3) Control cabinet
The control unit consists of a PLC cabinet and a power control cabinet. The PLC cabinet mainly performs the system's control tasks and includes the PLC host, communication module, input module, and output module. After receiving the given and feedback signals, the PLC host performs logical operations according to its internal program, controls each output point according to the design requirements, and the actuators implement the specific actions. The power control cabinet mainly performs the tasks of powering the system, the protection system, and the hydraulic system pump station motors , and includes circuit breakers, phase loss detection units, and motor protection devices.
When the operator issues a start command for the oil pump, the programmable logic controller (PLC) energizes the coil KM of the contactor for the main variable frequency motor of the pump station. The main oil pump motor starts working, and once the oil pressure rises to the design requirement, it automatically notifies the operator. The operator can then select a stage effect; for example, pressing the "rise" command will raise the stage. Once the selected stage unit reaches its designated position, it sends a signal to the PLC. Upon receiving this signal, the PLC starts the maintaining oil pressure sustaining pump motor. Once the sustaining pump motor is operating normally, it disconnects the main oil pump motor, which then stops working. In this way, the main oil pump motor only operates when the stage unit rises and falls, and oil pressure maintenance is achieved through the sustaining motor, reducing noise and saving energy. The oil pump motor control flowchart is shown in Figure 4.
Figure 4. Oil pump motor control flowchart
2.4 Composition of the table motion control circuit
The stage control circuit consists of the stage, fork arm transmission mechanism [4], hydraulic transmission mechanism [3], PLC, and upper monitoring computer [5]. The schematic diagram of its control circuit is shown in Figure 5. The operator sends a given command to the PLC through the human-machine interface . The measuring device monitors the stage lifting and rotation position in real time. The detected value is compared with the given value. The PLC performs logic calculations and commands the execution mechanism to drive the stage lifting or rotation.
Figure 5. Schematic diagram of the control circuit for the platform
3 Control System Design
3.1 Countertop Dimensions
(1) The lifting platforms 1# to 5# are located at the rear of the stage, with dimensions of 3700mm×3000mm. The net lifting height of the main platform is 1200mm, and the platform closing height is 600mm. The unit stages are arranged in a single row of five columns and installed on the ground plane.
(2) The No. 6 passageway platform is located between the rotating platform and the stepped platform, designed to facilitate actors' smooth movement from the platform to the rotating platform during performances. When an actor ascends the rotating platform, the passageway platform descends to be level with the ground. The platform dimensions are 1800mm × 940mm, the net lifting height is 1200mm, the closed platform height is 600mm, the static load of the stepped platform is 300kg/ m² , the dynamic load is 150kg/ m² , and the lifting speed is 2400mm/min. The rotating platform and the passageway platform are decorated with plexiglass. The passageway platform and the rotating platform form an interactive lifting system, creating various three-dimensional artistic effects on the rotating platform.
(3) The No. 7 rotating platform is located in the middle of the intelligent stage. The platform size is Φ3600mm, the static load is 400kg/ m2 , and the dynamic load is 150kg/ m2 . The net lifting height is 1200mm, the lifting speed is 2400mm/min, and the rotation speed is adjustable from 600 to 4000mm/min. The minimum height is 600mm, and the platform can rotate in both directions.
(4) The front of the intelligent stage has a telescopic and lifting stage [6], namely stage #8. The telescopic stage has a platform size of 3700mm×5400mm (composed of 3 platforms of 3700mm×1800mm), with telescopic distances of 1800mm, 3600mm and 5400mm respectively; the base height of the telescopic stage is 450mm, and there are 3 lifting platforms on the stage with a platform size of 3700mm×1800mm and a lifting height of about 150mm to be level with the fixed platform; the static load of the telescopic platform is 300kg/ m2 and the telescopic speed is 2000mm/min. The fixed stage has a size of 20000mm×9600mm, a height of 600mm, a load of 500kg/ m2 , and is made of steel frame and wood. The platform steps are 3700mm×300mm×150mm in size and have a static load of 300kg/ m2 .
3.2 Control Procedure Flow
In the control system, the stage platform is a very special controlled object. Compared with the hydraulic transmission mechanism, it has a large mass, ranging from several tons to tens of tons. The movement of the platform is consistent with the movement of the fork arm, and its transfer function can be approximated as a proportional element. Since the time constant of the hydraulic transmission mechanism is not large, a logic control strategy is adopted here. Because the decision-making principle of the telescopic lifting platform and the rotary platform is the same as that of the lifting platform, the control principle of the lifting platform will be explained using it as an example.
According to the on-site requirements and technical specifications of the broadcasting center's studio, the closed height of the five lifting platforms is required to be 600mm, and the net lifting height is required to be 1200mm. The entire lifting process is completed in four stages, with each stage being 300mm high. Each lifting platform can either rise and fall to the designated height all at once and then stop, or it can rise and fall in stages, that is, rise and fall only 300mm at a time and stop, rising and falling multiple times to reach the designated height. The five lifting platforms can rise and fall to the designated height simultaneously. The platform height is given as a value i, and five height values are assigned to five variables according to the four stages: imax=1200, imid+=900, imid-=600, imin=300, i=0. The following uses the stage of lifting unit #1 as an example to illustrate its specific working process, and the program flow is shown in Figure 6.
Figure 6. PLC network topology diagram
3.3 Control System Hardware Equipment
The 800m² studio's intelligent stage mainly consists of a front-area telescopic T-shaped stage, a central-area rotating and lifting stage and aisle lifting stages, a fixed stage, a rear-area stepped lifting stage, an electrical drive and hydraulic transmission system, and an intelligent control system and software. The control system hardware is listed in the attached table. (Attached Table: Basic Configuration Table)
3.4 Statistics of Control System Monitoring Points
The design requirements for the stage control system of the 800m² studio unit in the broadcasting center described in this article require a total of 96 monitoring points, including 57 input points and 39 output points.
According to the design requirements of the 800m² studio stage of the Broadcasting Center, one S7-200 PLC will be used, with the following configuration:
(1) CPU226 1 host
(2) EM223 3 (expansion modules)
(3) EM232 1 (expansion module)
The CPU226 controls the frequency converter of the pump station motors, enabling the rotation of pump stations 1 through 3 and the rotary table. Output point 1 of EM223 drives the lifting movements of lifting platforms 1 through 5; output point 2 of EM223 drives the lifting movements of the rotary table and the access platform; output point 3 of EM223 drives the telescopic T-shaped platform's extension and retraction and lifting movements. EM232 is a backup. The PLC network topology is shown in Figure 7.
Figure 7. Flowchart of Stage Lifting Procedure (No. 1)
4. Monitoring of the control system
The stage movement control system utilizes network communication technology, making system monitoring simple and convenient. There are two operating methods for controlling the stage movement: one is via a touchscreen, and the other is monitoring and operating using host computer configuration software.
Based on the Windows platform, MCGS is an integrated human-machine interface system and monitoring management configuration software system. It can complete functions such as field data acquisition, real-time and historical data processing, alarm security mechanisms, process control, animation display, trend curves and report output, and enterprise monitoring network, and quickly construct and generate upper computer monitoring systems.
The intelligent stage motion control system monitoring software uses MCGS industrial control configuration software and employs Siemens PPI communication protocol and RS-232/485 converter for convenient and fast communication with S7-200. To meet the requirements of the stage motion monitoring system, this paper designs a main display screen that records the changes and trends of key parameters in real time and allows for convenient parameter settings; improves the safety performance of the monitoring method; and can completely record alarm time, alarm type, etc., facilitating error checking by staff.
The above introduction pertains to the connection between the PLC and the MCGS configuration software in the industrial control computer. In the unit stage control system, the host computer also includes the Delta touchscreen manufactured in Taiwan, as mentioned in the previous section. The two control systems have the same functions but different applicability; the touchscreen's jog function complements the preset program function/real-time programming function/random manual control function.
The main screen of the stage monitoring system is the first screen displayed when the administrator enters the password to access the stage monitoring system. The names of the various sub-screens on the main screen are dynamically linked to their corresponding sub-screens, as shown in Figure 8.
Figure 8. Main screen of the monitoring system
Taking the main lift platform screen as an example, the main lift platform control interface is explained, which includes five lift platform operation screens located at the rear of the stage platform. This screen allows monitoring of the individual movement status of each of the five lift platforms. It accurately reflects the changes in the lifting direction and height of each lift platform, while precisely displaying the lifting height. It also allows for coordinated operation of the five lift platforms. The main lift platform screen is shown in Figure 9.
Figure 9 Main lifting platform view
5. Conclusion
An intelligent stage motion control system was analyzed and designed. Utilizing Siemens S7-200, the system met the requirements of the performance, increased the variety of performance scenes, enriched the performance effects, and demonstrated significant economic and socio-economic benefits. Field practice has proven the design scheme to have excellent control performance.
Edited by: He Shiping
