Hello everyone, I am currently facing a unique challenge while working with a customer's Direct Logic 06 PLC system. The customer's setup includes a DC motor running at 10 RPM, connected to a shaft with a notch. A Keyence fibre optic unit is positioned to detect when light passes through the notch as the shaft rotates. The Keyence unit outputs an analog signal based on the amount of light passing through the notch. The goal is to stop the motor when the Keyence unit reaches its peak voltage output. The customer prefers to use the "peak" voltage rather than a preset number, as external factors such as light values or dirt may cause variations in the set value. Therefore, the motor should be stopped when the Keyence unit reaches the highest voltage for that specific rotation. Your assistance in solving this challenge would be greatly appreciated. Thank you, Bill.
The concept of "peak voltage" refers to a specific time period during which multiple voltage samples are taken across various motor positions. The ultimate peak voltage value cannot be determined until the final sample is collected. If the final sample does not represent the peak voltage, it indicates that the motor has surpassed the peak voltage position and needs to rotate in the opposite direction. But is the motor capable of doing so? How are motor positions managed and what role does inertia play in this process? Additionally, noise interference can make this task more challenging. Perhaps it is feasible to outline a strategy for approaching peak voltage and forecasting the next peak voltage position, but having control over the motor position in both directions would likely offer more advantages.
Hi Bill, I'd suggest setting up your PLC program to incorporate a reset and record function at each rotation of the shaft. This function should register the peak voltage during each individual rotation, resetting after each complete turn. If there's concern about factors like ambient light or dirt affecting the values, you could potentially use a complementary sensor to correlate and counterbalance such external factors. Try a few dry-run tests to establish a range of values that would signal the notch's position accurately. Don't forget to simulate some "dirty" conditions as well while testing; varying light levels, introducing particles, etc. would provide a more robust solution.
Hey Bill, interesting problem you've got there! What you are looking for is essentially implementing a peak detection algorithm on your PLC. To achieve this, consider using a simple software approach: Monitor the voltage input continuously and compare it with the previous cycle's peak value. If the voltage signal begins to fall, that means you've crossed the peak and you can stop the motor. Be sure to reset this peak value after every shaft rotation or at the start of a new cycle. One will have to factor in debouncing or damping techniques for accurate peak detection, considering the noisy nature of an analog signal from such sensors. Do update us with your progress!
Hi Bill, one possible solution could be to use a programmable peak detection algorithm in the PLC. Essentially, this will compare the current voltage reading from the Keyence unit with the last one. If the current voltage is greater than the last, the code could overwrite the previous peak value with the current one; if it's lower, then the code would assume that the unit has passed its peak and could output a control signal to stop the motor. To avoid false positives caused by noise or minor variations, you might want to include a small hysteresis in the code (i.e., the voltage must decrease a certain amount below the peak before the code acknowledges it as a true peak). Keep in mind, this is a rough skeleton of a solution, and you'd need to tailor it to your specific application.
Hey Bill, very interesting problem you've got. I would suggest utilizing the PWM or PID features found in most PLCs including the Direct Logic 06. Basically, first, you need to continuously sample the values from the Keyence unit. Then, script your PLC to monitor the trend in the Keyence voltage output, noting when it stops increasing and starts decreasing - that's your peak. Even considering external factors, this should give you a fairly accurate peak detection to base your motor stoppage on. It'll require a bit of trial and error to program, but should solve your challenge.
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Answer: To stop the DC motor at peak voltage detected by the Keyence fibre optic unit, you can program the PLC to monitor the analog signal output by the Keyence unit and stop the motor once the signal reaches its highest voltage for that specific rotation.
Answer: Stopping the motor at the peak voltage detected by the Keyence unit allows for greater precision and adaptability in response to external factors like varying light values or dirt that may affect the signal output. This approach ensures that the motor is stopped at the optimal point for each rotation.
Answer: By monitoring the analog signal output by the Keyence fibre optic unit in real-time and dynamically adjusting the stopping point based on the peak voltage detected for each rotation, you can account for variations caused by external factors and ensure accurate motor control.
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