Cognex Helps GM Canada Develop a Chain Drive Based on Vision Sensors https://www.automation.com/files/pluginfiles/item_99536/field_376/GM-Chain-Link-Picture1_reg.png
29. October 2018 - Chain drives are a critical component of the manufacturing process in many industries, whether the chains serve as conveyors for glass containers or as means of transport frames kilometer-long production lines. But regardless of the industry, the vibration and constant pull on the chain links can stretch, distort and even break the weakened links if improperly serviced, resulting in unplanned downtime and productivity and profit losses.
The traditional dependence of the automotive industry on chain drives has led production engineers to look for better ways to monitor chain drives. Until recently, automakers inspected each link with a metal rectangle the same length as a new chain link. A technician visually checked each link for correctness. If a connection was problematic, the technician tagged the chain and hoped it would continue to work until the next scheduled maintenance. In the meantime, if the chain broke, expensive downtime occurred until the chain could be repaired.
In collaboration with Cognex, engineers at General Motors of the Canada Company (GM Canada) have developed a chain drive system that measures each link in real time and automatically marks non-compliant links without slowing or stopping the line. Following the rejection of a solution using discrete photoelectric sensors combined with laser pointers to measure link lengths, GM Canada engineers developed a real-time chain monitoring system based on a Cognex In-Sight 2000 vision sensor.
The In-Sight 2000 solution uses red LED illumination to illuminate the chain to give an overview of the connection being tested, while a complementary red filter helps to eliminate the effects of ambient light. A proximity sensor provides the trigger signal to the camera as each link passes within its field of vision (Figure 1)
Figure 1: Cognex In-Sight 2000 camera scanning a chain link
The In-Sight Explorer image processing software from Cognex takes the images and performs edge detection algorithms to identify the center of each chain link, and then uses a measurement tool to measure the inner length of the chain (Figure 2)]
Figure 2: In-Sight software in "easy builder view" for chain stretch monitoring. The middle picture shows a chain link and its inner length. The top right column shows the In-Sight Explorer algorithms used in the inspection process, while the bottom section shows the pass / fail result for each chain connection.
Basic pass / fail inspections can be performed with an intuitive point-and-click setup tool, "says system designer Christopher Eid of GM Canada's Electrical Engineering-Paint Department, in which case edge detection is used If both edges are found, the distance between the two links is measured, and the result is placed under the respective category of the chain stretch limit, and the result is sent to the PLC, which then uses communicates with the HMI and displays the relevant information. "
With caliper measurement, GM Canada's system determines the percentage of all connections to the norm. When the deviation reaches 4% or more, the vision system sends a signal to a nearby PLC via an optional Cognex I / O module. It counts how many links fall into each category and the number of revolutions for a 1,680 foot chain (Figure 3)
Figure 3: HMI for control and display chain Stretch Results
The PLC allows the user to measure connections the first time a conveyor magnet (reference point) is detected by pressing "Start Now" or by discrete scanning. The user can also decide how many revolutions of the conveyor chain the Cognex system should measure during a review session.
"So far, we have tested the system on our fastest conveyor belt," explains Eid. "We started with a coverage of 70% because the camera runs faster than the PLC, today we do most of the analysis on the camera, and we use a 9-frame buffer bit on the Cognex vision sensor with the camera We can cover more coverage per scan, and based on the success of the system, we plan to roll several more systems in the near future and eventually modify the system for paint shop transfer chains. "
According to Eid, the PLC may be a downstream paint sprayer Control Mark chain links that fall in the 4-5% expansion category for replacement during the next scheduled maintenance cycle.
How vision sensors like the Cognex In-Sight 2000 gain the speed and performance to keep up with the fastest industrial applications Engineers realize that mating discretely wired "stupid" sensors and software is a waste of time and effort There is money, especially when the cost of capturing and using image sensors is balanced against the normal cost of unplanned downtime.
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