Faster, more stable, more powerful
--ProV Real Time's ultimate pursuit of sports and visual interaction performance
In many high-speed automation applications, the requirements for the interaction speed and stability of machine vision and motion control are getting higher and higher. Simply put, it is required to acquire images, process images, and control the results and motion to interact with data within a certain cycle period within a certain period of time. In order to ensure the smooth execution of this process, it is not suitable to use an operating system such as Windows, because such an operating system contains an internal mechanism that can introduce infinite delay, which leads to the unpredictability of the interactive process. For example, applications such as high-speed surface mount, precision assembly based on visual servo technology, and special-shaped battery stacks popular in recent years, Windows-based visual guidance, are facing greater challenges in terms of execution stability, yield control, and cycle time optimization. There are more and more challenges.
In order to meet the requirements of high-performance visual guidance systems, advanced automation systems need to introduce real-time operating systems (RTOS). Unlike operating systems such as Windows, real-time operating systems allow designers to accurately predict system jitter—start time and time to complete tasks, such as image acquisition, processing, and I/O control. Although real-time operating systems can be used for such tasks, they are usually combined with general-purpose operating systems such as Windows. In this way, developers can use ready-made development kits to implement functions such as graphical user interfaces, and at the same time use real-time operating systems to implement time-critical tasks.
ProV Real-Time (ProV RT for short) is a real-time visual guidance system based on RTOS and Microsoft Window developed by the ProU team. It migrates the GigE protocol for image acquisition to the real-time system. At the same time, the image algorithm and alignment calculation are also completed on the real-time system. Through real-time interaction with the motion control module based on RTOS on ProU winPLC, an exciting fast and stable visual guidance application is realized. The system composition and functions of ProU winPLC are shown in the figure.
From the perspective of the entire visual guidance process, from the beginning of the camera command, the camera's drive call, image transmission, query completion, image processing, communication, and motion control all links require Windows intervention, which is the source of system delay. Through a large number of experiments and data analysis, we have recorded the possible delays due to the intervention of windows. Compared with ProV RT, the overall execution time will be longer and the uncertainty will increase.
The fixed time overhead of image transmission and processing continues to exist. The analysis of the entire process is shown in the figure below.
Through specific cases, it can be seen more clearly that the difference between ProV RT and traditional solutions based on Microsoft Windows operating system (see the figure below).
The winPLC controller controls 3 Raise closed-loop steppers through the EtherCAT bus, and a Daheng 500MP/GigE industrial camera is connected to the ProV RT module on winPLC. winPLC performs visual alignment and motion control at the same time, and is applied to common image tools such as calipers and blobs. Image processing and transmission are completed in a real-time system (RTOS). On the ProV RT platform, users can realize image processing and alignment calculations by dragging and dropping the block diagram, and transfer the calculation results to the motion control module on the ProU platform.
For comparison, we use the H image algorithm library and the G motion control board to achieve the same image algorithm and motion control. The data comparison is shown in the figure below.
The continuous image transmission and processing is about 2000 times (as shown in the figure above), and the average time consumption of ProV RT is reduced by about 10%. The more obvious difference lies in the stability of the execution cycle. It can be clearly seen from the above figure: There are several spikes in the Windows-based visual execution cycle, and the longest execution cycle reaches 540ms.
For a complete test-2000 consecutive visual guidance alignments (as shown above), the execution efficiency of ProVRT can be increased by about 20%. It can be seen from Figure 5 that the biggest difference between the two systems is the stability of the execution cycle: Windows-based motion control and vision systems will have a delay of up to about 1080ms in some cycles. For machines pursuing high-speed and stable execution cycles, a delay of 1s is likely to bring real problems such as downtime, lower yield, and process verification failures.
ProV RT is an open real-time vision platform. Image algorithm companies can put their own image algorithms in ProV RT for execution, and directly call the motion control module in ProU. At present, ProV RT has demonstrated its unique value in several scenarios with extreme performance requirements and stability requirements, such as high-speed surface mount and precision assembly based on visual servo technology.