Design of automobile sensor test system based on flexible test technology

At present, the control system used in automobiles can be divided into three parts from the functional point of view: sensor unit, control unit and execution unit. Among them, the sensor unit is the symbol of automobile intelligence and has a unique and important position. The quality of the sensor unit directly affects whether the other parts of the automobile can be effectively monitored and controlled, thereby affecting the overall performance of the automobile. Therefore, sensor manufacturers or vehicle manufacturers need a means to evaluate and verify the sensors before they leave the factory or are installed in the vehicle.

Automobile sensor testing has its own characteristics, mainly including:

(1) The diversity and rapid changes of the objects being measured.

Commonly used sensor types in automobiles include wheel speed sensors, crankshaft/camshaft position sensors, temperature sensors , pressure sensors, knock sensors, etc. In view of the endless emergence of new models, each sensor with the same function has various differences in appearance. In addition, the requirements for measurement indicators and production environment are becoming more and more stringent, making it impossible for the traditional single test bench to take into account the production of such a variety of sensors.

(2) Similarity of test content.

In actual production, the test contents of different sensors are somewhat similar. This is because from the perspective of test principles, automotive sensors are mainly divided into active/passive, temperature, pressure and other types. In other words, for different sensors, as long as the test principles are the same, it means that their test instruments and other equipment are also the same.

(3) Efficient and flexible testing equipment.

Automotive sensor production lines require economical, efficient, automatic, and flexible testing equipment, and must have the characteristics of high automation, high efficiency, high productivity, and high reliability. Sensor manufacturers hope that after a one-time investment, the testing equipment itself can be continuously expanded to effectively support the latest products and higher performance index requirements, thereby ensuring the effectiveness of equipment capital investment.

(4) Other requirements.

In order to ensure production quality, the equipment needs to have certain production process statistical capabilities and help reduce the problem of reduced production quality due to human factors.

Integration and intelligence are the development trends of automotive sensors. If only final inspection tests are performed, it will be too late to find problems, so the test is often conducted interactively with the production process. In this way, on the one hand, the test equipment is required to be well connected with other equipment on the production line, and on the other hand, information and data sharing between equipment can be achieved.

In summary, the production test of automotive sensors no longer requires a few simple test instruments, but a set of mechanical, electrical and soft, automated, easy to expand, and open test equipment. These are exactly what the Flexible Testing technology advocates. Practice has proved that the automotive sensor test system designed with flexible technology meets the requirements of sensor final inspection.

Flexible testing technology

In fact, with the advancement of science and technology, not only automotive sensors, but also various other electronic devices are becoming increasingly intelligent and complex to meet consumers' requirements for comfort and ease of use. Under this circumstance, Panhua Measurement & Control, based on summarizing past experience, has proposed a series of solutions for the production testing of electronic products, called flexible testing technology.

Flexible testing technology is a technology that relies on related technologies to meet the needs of testing and measurement. Modern testing technology is centered on virtual instrument technology, test and measurement technology, mechatronics technology, software technology, and communication and network technology, and has the following characteristics:

(1) Adaptability: meet the requirements of various test environments, provide a variety of test performance, and integrate multiple signal testing capabilities;

(2) Flexibility: Change the functions and performance of the test system according to customer needs and apply a variety of technologies to meet test requirements;

(3) Scalability: Follow the development of related technologies to ensure the advancement of application systems and achieve continuous improvement in testing capabilities.

The automotive sensor testing system is built based on flexible testing technology. During many years of actual product development, the advantages of flexible testing technology have been fully demonstrated.

Flexible technology helps sensor test system design

With the help of flexible testing technology, Panhua Measurement & Control has developed sensor testing systems for wheel speed, position, knock, pressure, temperature, etc. These testing systems focus on virtual instrument technology, interface standardization and component modularization, mechatronics, network technology, etc. The following are examples of 3 automotive sensor testing systems.

Example 1: Wheel speed and position sensor test system

The dynamic/static parameter measurement of the vehicle wheel speed and position sensor is the core content of the test system. The system needs to have high test accuracy and repeatability, and some test parameters need to be customized according to the actual situation. Virtual instruments are test and measurement systems based on computer technology, which can meet the software/hardware requirements of the above systems, so virtual instruments are selected as the technical means of development. In addition, the system needs to provide an I/O interface to control external actions, and a motion control card is required to accurately control the speed. It is a flexible system that combines electromechanical and software.

In the system principle, the core of the sensor test system is the PXI system, which is mainly composed of a controller, a multimeter module, an oscilloscope module, a digital I/O module, a motion control module, a matrix switch module, etc. The PXI system transmits data through the PXI bus.

(1) The controller realizes human-computer interaction through 显示器\'); companyAdEvent.show(this,\'companyAdDiv\',[5,18])"> the display , mouse, and keyboard.

(2) The multimeter module and oscilloscope module can test the resistance, current, inductance and capacitance of the sensor under test by switching the matrix switch.

(3) The function of the digital I/O module is to control the cylinder, alarm system and indicator light, and monitor the status of the test start switch, photoelectric sensor, etc.

(4) The motion control module mainly controls the movement of the servo motor so that it drives the target wheel to operate according to the set parameters and stimulates the sensor under test to generate a signal.

(5) The matrix switch module is used in conjunction with the multimeter module and oscilloscope module to complete the switching of sensor signals, power supply, and gap signals to different devices. [page]

In addition, the power supply is controlled by the computer to provide the power supply requirements of the sensor under test .

At present, there is no unified industry standard for automobile wheel speed and position sensors. They are basically customized according to user requirements. For example, the target wheel and its rotation speed, air gap and sensor installation dimensions are different. Even if the sensor is installed on the same type of vehicle, there will be some differences due to different installation positions.

It is impossible for the same device to meet the test requirements of all sensors, so the modular design concept is introduced, that is, the same parts of the system, such as test instruments, test software, pneumatic control systems, and main circuit systems are used as common resources (host); for the parts of the system that are required to change with the sensor, such as target wheels and motors, fixtures, and special circuits, they are all in the form of modules. The electrical connection between the host and the module is completed by quick plug-in, and the interface is standardized to meet subsequent expansion needs. When testing different sensors, different test modules can be selected and connected to the host.

The wheel speed and position test contents are roughly the same, but there are also some differences, so the test software should be able to add, delete and edit the test contents within a certain range. Therefore, a custom script file (including various port allocation information, test contents and test steps, etc.) is designed, and the software performs operations according to this script file. Providing corresponding script files for the tests of different sensors can solve the problem of software reuse.

In addition, the system is designed with special dedicated circuits placed on different modules. When the module is inserted into the host, the software will automatically correspond to the inserted module according to the dedicated circuit on the module, and automatically call out the corresponding test parameters, making module replacement more convenient and quick.

Example 2: Knock sensor test system

The knock sensor test system is mainly composed of an operating table and a control cabinet.

In the principle of the test system, the vibration test adopts the relative method to realize the sensitivity test of any frequency point in the frequency band of 3000~40000Hz for the automobile knock sensor, and can detect the capacitance, insulation resistance, etc. The test system adopts the PXI architecture, and realizes control and signal acquisition through PXI modular instruments or GPIB instruments.

Knock sensors, like wheel speed and position sensors, do not have unified standard requirements, but the test principles are the same, except that the appearance and test parameters of the sensors vary with different sensors. Knock sensors are generally installed on the vibration table with M8 bolts, so the differences in the sensor heads can be ignored. Different adapter interfaces are used for different interfaces to achieve fast model change.

The interface adapter is equipped with an identification circuit. When the test parameters are configured through the test program, the program will automatically call the test parameters corresponding to the interface adapter to prevent misoperation.

Example 3: T-MAP sensor test system

The T-MAP sensor is the intake manifold pressure- temperature sensor , which can assist in adjusting the injection amount and thus controlling the air-fuel ratio. It is a relatively important sensor on the car. The final inspection equipment needs to perform capacitance detection, NTC (thermistor) detection, Ramp test, Leakage test, etc. on the sensor.

T-MAP testing needs to be performed during the air pressure change process, which takes a long time and is difficult to meet the requirements of mass production. Therefore, the system is designed with a 3-station parallel testing method to occupy the test hardware and air pressure system resources in a time-sharing manner, improve work efficiency, and reduce hardware costs.

All actions during the test are driven by cylinders and completed automatically. The operator only needs to put the workpiece into the fixture. After the test is completed, the workpiece is transferred to the next station by the conveyor belt.

Taking into account the scalability of the system, the parts that will change with the object being tested are designed with modularization and interface standardization. In the case of product incompatibility, corresponding test modules can be added.

In addition, as a final inspection device, the system needs to share data with other production equipment. On the one hand, the necessary parameters required for the system test need to be obtained from the previous test equipment before testing; on the other hand, the test data needs to be placed on the server for use by other systems. Automatic conveyor belts and I/O signals are added to the structure and electrical to realize the automatic transfer of workpieces between the previous workstation and the subsequent coding equipment. Therefore, this equipment has been organically integrated with other equipment on the production line to form a set of production and testing lines.

Conclusion

Flexible testing technology is a culmination of multiple technologies, focusing on meeting the needs of different production applications. The automotive sensor testing system based on flexible testing technology embodies the design ideas of structural modularization, electrical interface standardization and software componentization, and organically integrates multiple technologies such as mechatronics technology, virtual instrument technology, and software technology, so that the three advantages of testing technology, namely flexibility, adaptability, and scalability, are fully reflected.