Hello everyone! I've encountered an intriguing challenge and I'm hoping some experienced professionals can lend their expertise. I'm currently working on a project involving two hydraulic cylinders that operate alternately to dispense slurry, which is utilized in the production of foam components for vehicles. This foam material, often found beneath the hood, serves to reduce noise and encase Freon lines. These hydraulic cylinders are part of a system that mixes additional materials following the slurry dispensing process. The mixed material is then directed through a mixhead and dispensed into a mold, all managed by a robotic setup that I do not control. My primary responsibility is to program the PLC to ensure these cylinders dispense a precise volume in grams within a specific timeframe in seconds. Rather than implementing a PID controller, the company utilizes HACD controllers from Rexroth, of which we are a certified distributor. My pressing question is this: the cylinders are struggling to dispense a consistent amount of slurry and have yet to reach the desired weight setpoint of 36 grams per second. Each dispensing event is referred to as a "shot." We identified that two lines within the mixhead were blocked, and we also found that the mixhead itself was obstructed. The hydraulic cylinders operate within a limit of 1,500 psi, but the company asserts that this is not the source of the problem; they expect the shot volume to be accurate. The slurry normally circulates through the mixhead when not actively dispensing, but due to the blockage, I suspect the HACD controllers are unable to adjust quickly enough at 1,500 psi to achieve the desired volume. Has anyone else encountered similar issues with HACD controllers? I would greatly appreciate any insights beyond the extensive 722-page manual. Thank you for taking the time to read this, and I am looking forward to your valuable feedback. I've attached a spreadsheet used for volume/second calculations and a snippet of the logic intended for the HACD for your reference.
Thank you, everyone! I’ve successfully resolved the issue.
It's rare for this forum to be at a loss! What was the final outcome?
Absolutely! Please share the details of the correction with us!
It appears that the spreadsheet contains an error in the formula for calculating the area of a cylinder. Specifically, the formula fails to correctly divide the diameter by 2 to determine the radius. Additionally, there is some ambiguity regarding how the system manages the acceleration and deceleration of the two cylinders when one transitions to take over from the other. However, a generally effective approach is to synchronize their acceleration and deceleration levels while initiating the change simultaneously. This ensures a smoother operation between the cylinders.
It sounds like you're dealing with quite the technical challenge! From what you've described, it seems like the blockage in the mixhead is likely a significant bottleneck that's preventing the HACD controllers from accurately regulating the flow under pressure. Have you considered conducting a thorough cleaning of the mixhead and inspecting any potential obstructions in the hydraulic lines? Sometimes, even minor blockages can greatly affect performance. Also, since you're not using a PID controller, it might be worth looking into the tuning parameters of the HACD to ensure they're appropriately set for your specific application. Trying to gather more data on the response times and consistency of the slurry flow could provide valuable insights as well. Good luck, and I hope you find a solution soon!
It sounds like you’re dealing with a complex system, and those blockages definitely complicate things! One thing to consider is whether the HACD controllers can adequately compensate for the sudden pressure changes due to the obstruction, especially at those high pressures. Have you tried adjusting the response time settings within the HACD configurations, or perhaps even running some tests with different flow rates to see if that helps with the consistency? Also, while it’s great that the system circulates the slurry, if there's a viscosity change or if the material settles while waiting, that could be affecting your shot accuracy too. Exploring these factors could yield some positive results! Good luck!
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