We are in the process of developing CAM profiles for a link arm mechanical system, aiming to establish constraints on either load jerk or motor torque. Currently, we have a CAM that optimizes motor torque based on load inertia. However, this configuration requires us to operate the machine at maximum capacity, which isn't always feasible. Using Excel, I've been able to create CAMs that function well for acceleration; however, I'm struggling to determine when to initiate deceleration based on the current position and how much time it will take. If anyone could guide me in the right direction, I would greatly appreciate it. I remember encountering some equations from Peter Nachtwey several years ago, but unfortunately, I can't find them now. Your insights on CAM profile development, motor torque optimization, and deceleration timing would be invaluable!
Explore this discussion thread for valuable insights: http://www.plctalk.net/qanda/showthread.php?t=38759.
Tarik excelled at uncovering past discussions related to this topic. It's essential for me to understand the exact intentions of the original poster (OP). Many of these issues necessitate solving several equations with multiple unknown variables, making it crucial to approach the problem methodically.
Thank you for providing the link, Tarik. After spending several hours searching, I was unable to locate it. Regarding the link arm assembly, it facilitates the linear movement of a large structure into the machine. The operator has the ability to choose how far the arm extends into the machine; it doesn’t perform a full 360-degree rotation like conventional link/arm systems. Instead, it operates within a 170-degree range. When we employ a standard linear movement with the servo, the duration of the motion exceeds their desired timeframe. However, utilizing a CAM (Computer Aided Motion) optimized for torque enables us to considerably reduce the motion time. A challenge arises, though, when the machine operates at lower speeds; at that point, the CAM can lead to torque oscillation due to reduced inertia. My ultimate objective is to program the PLC (Programmable Logic Controller) to execute the necessary calculations and subsequently upload the CAM into the servo system. I acknowledge that the mathematical requirements are significantly more complex than what traditional PLCs typically manage, so I plan to limit the number of calculations per PLC scan and take several seconds to reconstruct the CAM.
When adjusting tuning, it's essential to account for changes in inertia. The torque generated is generally proportional to the angular acceleration. The goal is to effectively compress the duration of the cam table until the torque or acceleration thresholds are met. Due to the interconnected nature of cubic splines, optimizing motion isn't straightforward; it requires an iterative approach. A practical strategy involves decreasing the time intervals between all points until you reach the acceleration limit. Typically, one specific point often becomes the constraint, but a more effective optimization technique involves minimizing the gaps between all points. However, it's important to note that modifying one point, like point 3, can impact others, such as point 7. This challenge is complex, but there are optimization and minimization algorithms available that excel in these types of scenarios, although they may require some fine-tuning to achieve optimal results. Once you master this process, your perspective on mechanical tuning and optimization will dramatically transform. For further insights, consider exploring the Nelder-Mead simplex method. Learn more here: https://en.wikipedia.org/wiki/Nelder–Mead_method.
Thank you for providing the valuable information.
It sounds like you're on the right track with your CAM profiles! For determining when to decelerate based on position, I'd recommend starting with a simple distance-to-target ratio—monitor your current position and set a threshold at which to initiate deceleration, perhaps using a percentage of the total distance left to travel. This way, you can dynamically adjust the deceleration phase based on real-time feedback. Also, if you’re trying to balance between torque and load, consider implementing a timing function that incorporates both your motor feedback and load measurements to predict when to ease off your acceleration. If you have access to simulation software, that could be a huge help in visualizing these transitions before you implement them. Keep experimenting with your Excel models; it's a great tool for refining those calculations!
It sounds like you're dealing with a complex challenge! One approach to initiate deceleration could involve calculating the distance to the target position and factoring in your system's current speed and the desired stopping distance. You might want to explore implementing a PID controller, which can help fine-tune your deceleration profile based on real-time feedback. As for optimizing motor torque, it might be beneficial to run simulations at varying load conditions to determine a more efficient operational threshold rather than max capacity. If you can, try reaching out to Peter Nachtwey directly or checking engineering forums where his work might be cited; you might find the equations you need! Good luck, and I hope you find the right balance for your CAM profiles!
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