1 Introduction
Currently, the high-end dental chair equipment market is basically monopolized by foreign companies, whose products are generally expensive and whose technology is not transferred. With people paying increasing attention to oral health, developing high-end integrated dental treatment systems suitable for China's national conditions is particularly necessary. The dental chair controller is the core of an integrated dental treatment system; its design level reflects the degree of automation of the entire system and is also an important criterion for judging the quality of the dental chair.
This paper studies and develops a dental chair control system based on ARM embedded technology. By applying an embedded operating system to the control system and utilizing functions such as multi-task management, inter-task synchronization, and communication, the system's reliability and real-time performance can be further improved, enhancing intelligent control and management capabilities.
2. Overall Functional Overview
The overall system block diagram is shown in Figure 1. The design of the dental chair control system must meet medical needs and be easy to use and operate. In practical work, a high-end dental chair must not only support movement in four basic directions (up, down, supine, and reclining), but also be able to perform functions such as dispensing water from a teacup, rinsing the sputum cup, adjusting the shadowless lamp, acquiring position data, transmitting X-rays, and communicating with a host computer. It must also ensure smooth and reliable movement and real-time data transmission. The dental chair control system's CPU responds to external keyboard input, executes corresponding commands, and drives the external hydraulic transmission mechanism to realize the movement of the dental chair and the operation of other external devices.
Since the dental chair control system has many control points, which are concentrated in the instrument panel and the base of the dental chair, this paper divides the dental chair control system into three main modules: panel control module, base control module, and power supply module.
2.1 System Hardware Design
Based on requirements for chip performance, power consumption, and system specifications, this system employs a dual-CPU module consisting of an S3C44B0X chip and an ATmega16 chip for collaborative control. The S3C44B0X is a 16/32-bit RISC processor manufactured by Samsung, using a Samsung ARM CPU embedded microprocessor bus architecture. The S3C44B0X provides comprehensive and general-purpose on-chip peripherals, including an LCD controller, five PWM channels of timers and one internal timer channel, 71 general-purpose I/O ports and eight external interrupt sources, an eight-channel 10-bit ADC, and an SPI synchronous data communication serial ARM embedded dental chair control system interface. It offers excellent scalability and serves as the main processor for the dental chair system.
The ATmega16 is a low-power 8-bit CMOS microcontroller with an enhanced AVRRISC architecture. It has abundant internal resources, including 32 programmable I/O ports, 512 bytes of EEPROM, four-channel PWM output, eight 10-bit ADC conversion channels, three internal timers/counters, and an SPI synchronous data communication serial port. As the core and control chip of the base module of the dental chair system, it controls the movement of the dental chair and performs position data acquisition.
The schematic diagram of the dental chair control system is shown in Figure 2. The base control board CPU is connected to a 3×2 foot pedal keypad. The CPU receives input from the keypad, executes corresponding commands, and controls the on/off state of the hydraulic transmission control relays on the base module, controlling the movement of the dental chair in four directions (up/down), the rinsing position, and the treatment position. Considering user safety and the stability and reliability of the dental chair equipment, the CPU must monitor the feedback information from the limit switches in the four directions and the obstacle protection switch on the base in real time during movement and take corresponding protective actions.
To ensure ease of use, the panel control module must also be able to control the aforementioned movements of the dental chair and memorize its position in real time. Therefore, the system needs to achieve real-time communication between the base plate and the panel. Combining the characteristics of the CPU chip and actual requirements, both utilize a Serial Peripheral Interface (SPI) for high-speed synchronous data transmission. The panel CPU can receive input from an external extended keyboard to execute corresponding commands, and an expansion interface is reserved.
Since external devices are all high-voltage control components for the CPU, an opto-isolation circuit is added to the panel control module to maintain control signal communication while avoiding electrical interference—that is, to implement low-voltage and high-voltage isolation. The digital brightness adjustment design of the shadowless lamp adopts a PWM method. The S3C44B0X has five timers that can provide PWM output. Because the shadowless lamp used in the system has a rated power of 50W and a rated voltage of 12V, operating at high current, an IRF540 MOSFET is used in conjunction with the opto-isolation circuit in the control circuit to ensure the adjustment accuracy of the shadowless lamp.
2.2 System Software Design
Considering the future expansion of the system to include image acquisition capabilities and complex human-machine interfaces, the μC/OS-II operating system was ported to the S3C44B0X. μC/OS-II is a popular, free, and open-source real-time operating system. It not only features a small, firmware-enabled, customizable, multitasking, and preemptive real-time kernel, but its real-time performance, stability, and reliability are also widely recognized. The μC/OS-II kernel can be compiled to a minimum of 1.5KB , making it widely applicable to various types and sizes of embedded systems using microcontrollers ranging from 8-bit to 64-bit. Regarding memory usage, μC/OS-II is a customizable real-time kernel; the more tasks that need to be scheduled in an application, the larger the RAM space required.
Based on an estimate of running 20 tasks, the μC/OS-II kernel occupies less than 2KB of RAM space and can use 20 semaphores, mailboxes, etc. to complete the synchronization and communication between tasks.
The system uses the S3C44B0X's T0 timer as the operating system's clock source, with an interrupt frequency of 10ms. Every 10ms, the system calls a keyboard polling program to respond to keyboard events in real time. SPI communication between the serial port and the CPU uses interrupt-driven reception and transmission. As long as interrupts are not disabled, interrupt execution takes precedence over any other task to ensure real-time communication. Based on the control system's operational requirements, tasks can be categorized as follows: keyboard task, teacup water dispensing task, teacup water dispensing timer setting task, shadowless lamp task, LED indicator task, alarm information task, and spittoon flushing task.
Because communication between tasks, and between tasks and interrupts, is centrally managed based on semaphore mechanisms, a semaphore protection mechanism must be established.
In the initial task StartTask, a series of semaphores and mailboxes are first established:
Then, use the OSTaskCreate() function to create 7 tasks. Finally, delete the task itself in the starting task.
(1) Keyboard task: Call OSSemPend(Sem_Keyboard, 0, &err) to acquire a semaphore. After acquiring the semaphore, the task will call the mailbox message sending task OSMboxPost(OS_EVENT*pevent, void*msg) to wake up other corresponding tasks.
(2) Teacup Water Supply Task: Add water to the teacup. This task is initiated via OSMboxPost(Mbox_Cup, Msg_Cup).
(3) Teacup water dispensing timer setting task: Set the timer for dispensing water to the teacup. This task is activated via OSMboxPost(Mbox_CupSetting, Msg_CupSetting).
(4) Alarm Information Task: This task generates alarm information such as when the dental chair moves to an obstacle position and triggers an alarm, and performs corresponding processing. This task calls OSSemPend(Sem_AlarmTask, 0, &err) to obtain the semaphore.
(5) Flushing the spittoon task: Flushing the spittoon. This task is activated via OSMboxPost(Mbox_Ty, Msg_Ty).
(6) LED indicator task: The corresponding keyboard indicator lights are illuminated by dynamic scanning to indicate the current system working status. This task is activated by OSMboxPost(Mbox_LED, Msg_LED).
(7) Shadowless lamp task: switch on and continuously adjust the brightness of the shadowless lamp.
The task is invoked via OSMboxPost(Mbox_Move, Msg_Move).
In the system, task 1 is set to have the highest priority, followed by task 2, task 3 to task 6 in that order. The program flow is shown in Figure 3.
In the tasks described above, the CPU mainly accepts keyboard input to wake up other corresponding tasks. There are also tasks for recording the position and communicating with the host computer, which will not be described in detail here.
3. Control System Debugging Results
After long-term testing and operation in dental clinics, the dental chair control system was able to respond to inputs in a timely manner and move as required. The error in the returned memory position was controlled within 1mm, and the error in the teacup water level did not exceed 2mm. The results showed that the real-time performance and reliability of the communication between the control system and the host computer, as well as the communication between the two CPUs, met the design requirements. The entire system operated smoothly and reliably, was easy to debug and maintain, and improved the automation level and quality of the dental chair.
4 Conclusion
This paper enhances the system's functionality by employing an embedded processor and a real-time multitasking operating system, improving the system's reliability, real-time performance, and scalability. This facilitates subsequent expansion of image acquisition and human-machine interface functions, laying the foundation for further development of high-end products.
This dental chair control system can improve the domestic dental chair production and design level. It has been put into production in a medical device factory in Guangzhou, creating good economic and social benefits.
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