Four-wheel alignment systems involve knowledge from multiple fields, including mechanics, optics, electronics, computer software, and mathematical models. Structurally, a four-wheel alignment system mainly consists of a host computer and a slave computer. The host computer includes a housing, computer mainframe, monitor, printer, software, and communication system. The slave computer consists of measuring sensors, fixtures, and a cornering plate. The housing, located at the front of the four-wheel alignment system, contains the computer, printer, monitor, keyboard, mouse, and fixture sensors or fixture reflection plates. The computer mainframe is the carrier running the main program and can be a custom-built computer, a branded computer, or a commercial computer. The software, including the operating system and the four-wheel alignment system application, together with the computer mainframe, determines factors such as visibility, operability, functional stability, and measurement speed. The operating system can be Windows 98, Windows 2000, or Windows XP. The communication system can be wired, wireless, or Bluetooth, depending on the method used, which determines the ease of use. The measuring sensors are the rulers used to measure the four wheels of the vehicle, determining the overall measurement accuracy of the machine. This also reflects the technical attributes of the four-wheel alignment system. The sensor consists of a housing, a microcontroller motherboard, sensing elements (liquid, optical, or purely optical, and CCD), a communication system, and a battery. It uses many highly precise components, resulting in high cost. The fixture is the device that fixes the measuring sensor to the vehicle's wheels. The coordination between the four fixtures and the measuring sensor determines the accuracy of the measured values. Currently, the common detection methods for four-wheel alignment machines on the market are: laser, PSD, CCD, and 3D. Laser is a parallel beam of light. Because lasers output parallel straight beams, their beam measurement range is narrow, there is no compensation, and the thrust line needs to be manually calculated, resulting in low measurement accuracy and slow detection speed. Due to the relationship between light intensity and scale, and because lasers are easily affected by external interference, using lasers as a light source for four-wheel alignment machines is not ideal. Furthermore, lasers can damage human eyesight and have not received safety certification. PSD, also known as a photoelectric position sensor, works by changing the output current when light is illuminating a certain position on the PSD's light-receiving surface, thus determining the illuminated position. It is an analog device. It can only measure a single point of light. PSDs suffer from severe temperature drift and are affected by ambient light. Temperature changes can cause the output zero point to shift by tens of millivolts, and the influence of light makes the system values ​​unstable. These two factors combined cause PSDs to lose measurement accuracy and equipment stability. CCDs are semiconductor digital devices (also known as optocouplers), which are divided into linear CCDs and area CCDs. They integrate thousands of independent photosensitive elements on a silicon surface. When a laser beam shines on the photosensitive surface, the photosensitive elements collect photoelectrons, and through displacement, output the light, generating information about the light position and intensity. CCDs have no temperature coefficient, long lifespan, and good environmental adaptability. Currently, most domestic manufacturers use CCD measurement sensors, but these sensors require high machining precision, careful maintenance of electronic components, and periodic calibration. Manufacturing costs and component prices are also high. 3D measurement utilizes digital image recognition technology. A digital CCD camera captures image information mounted on a wheel image acquisition plate to measure the relative values ​​of the wheels. By moving the vehicle forward and backward, the CCD camera simultaneously captures information from the image acquisition plate. The computer calculates the coordinates and angles, and through software 3D reconstruction, the real-time 3D status of the four wheels can be displayed. This is a highly advanced measurement method that utilizes image recognition technology, requires no calibration, and boasts advantages such as high measurement accuracy, zero error, and simple operation (compared to four-wheel alignment machines, 3D reconstruction technology is already very mature and widely used in medical, industrial, public security, and military fields). Furthermore, the manufacturing cost is very low, requiring only two (four, one per wheel) CCD cameras and four image acquisition plates (low-cost components with no electronic components) and fixtures. The software also offers significant development advantages, enabling 3D reconstruction, animation adjustment, four-wheel structure display, tire diameter, real-time 3D measurement data, sheet metal body measurement, and photography functions. It can be integrated with computer inspection instruments, wheel balancers, engine analyzers, and vehicle body straightening machines via Bluetooth onto a single host unit. This is the future development direction; software can unlock more selling points for four-wheel alignment systems. In terms of production cost, 3D systems should be cheaper than CCD systems because they only use two digital CCDs, and the image acquisition board has no electronic components, requiring no maintenance. In contrast, CCD four-wheel alignment systems use four or eight CCD sensors. CCD measurement sensors also have microcontrollers, wireless Bluetooth communication systems, batteries, and other electronic components, leading to high failure rates and short lifespans. Even if 3D four-wheel alignment systems use high-pixel CCDs (professional digital CCDs) + professional acquisition cards and high-density image acquisition boards to improve measurement accuracy, it only increases the software computation load and cost. However, ordinary digital CCDs (industrial digital CCDs) are sufficient for four-wheel alignment systems (the measurement accuracy of CCD four-wheel alignment systems is more than 10 times higher) at a low cost. If software development costs are high, you can cooperate with major CCD and acquisition card manufacturers. They are image processing experts with their own software engineers to help you design the system. Collaborative development and self-maintenance allow for faster market entry and lower development costs. Currently, the market is dominated by CCD four-wheel alignment machines and other similar products, representing a huge market opportunity. Once 3D four-wheel alignment machines gain market share and become more affordable, they will revitalize the Chinese market. It is hoped that major four-wheel alignment machine manufacturers will soon move beyond CCD machines and enter the 3D product market, showcasing Chinese technology and reaping greater profits. Standardized automotive repair equipment is the key to the development of the automotive repair industry, benefiting car owners and ensuring national safety.