I am seeking advice on the optimal approach for a 2-position turntable control system (refer to the attached image). The turntable rotates 90 degrees before returning to its original position. It is equipped with a conveyor section for transferring products between adjacent conveyors. The SEW motor responsible for driving the slewing ring utilizes a PowerFlex 525 0.4kW VFD and is connected to an EK8S incremental encoder with 1024/4096 analog resolution, wired back to an Allen-Bradley 1734-IK POINT I/O 24V DC Incremental Encoder Module. What would be considered best practice for controlling the rotation and stopping positions in this scenario? Factors to consider include the use of inductive proximity switches, the utilization of incremental encoder technology, implementing overtravel protection, and incorporating a slowdown mechanism before reaching the desired position. I apologize if the details provided are vague; I am seeking feedback without divulging the current operational method for comparison. Should you require additional information, please don't hesitate to inquire.
Apologies for any ambiguity, I am seeking feedback without revealing the current operational method for comparison. Despite knowing the existing design, forum members frequently propose a redesign. Based on the visuals provided, it appears there is some flexibility in the angular positioning, making proximity switches a viable option for accuracy. However, if an encoder and corresponding module are already in place, it would be advantageous to utilize them. Consider the frequency and time constraints for the turntable movements, as well as the inertia of the loaded turntable to determine the acceleration and deceleration rates. The drive must be appropriately sized to handle the necessary current for load acceleration and dissipate kinetic energy during deceleration.
Set the destination position for the encoder and adjust settings for the speed difference to slow down or creep. Ensure safety with magnetic switches at In Positions A and B. Monitor the encoder closely, and if it overshoots the stop point, gently reverse it to the correct position. This method was successfully implemented on a hoist system with 2 position turntables and racks moving along a 22-station track. Initially, the hoist had proxy switches for proximity and speed adjustments, but they proved to be inadequate in stopping the hoist on time. Thus, adjustments were made by reprogramming and introducing a count system to fine-tune the destination position. Additionally, a feature was added to allow the hoist to creep back to the correct position in case of overshooting.
Steve Bailey mentioned that despite knowing the current design, forum members still suggested a redesign. Looking at the picture, it appears there is some flexibility in the angular position, indicating that proximity switches could provide sufficient accuracy. However, utilizing an encoder on the motor and corresponding module on the drive could be advantageous. Factors such as the frequency of turntable operation, time available for each move, and the inertia of the loaded turntable will determine the acceleration and deceleration rates. The drive must be adequately sized to handle the current needed for acceleration and dissipate kinetic energy during deceleration. Considering a combination of encoder positional feedback and proximity switches to establish position bands, like stopping at proxy A for position A and verifying the encoder count falls within a set range. Alternatively, stopping based on encoder count and then confirming with proxy activation could also be a method to consider. The turntable typically operates 600-900 cycles daily with a takt time of 56 seconds. Speed is not a priority, as cycles are currently completed within 30 seconds. The design is robust and over-engineered for its intended use, mitigating concerns about inertia and other mechanical variables. I_Automation suggested a methodology for controlling encoder destination positions, adjusting speeds, and utilizing safety magnetic switches for position verification. They shared their experience with similar setups involving turntables and hoists, emphasizing the importance of fine-tuning settings to ensure precise positioning. Considering the use of proximity switches for stop positions and encoder feedback for speed control, do you anticipate any issues with incremental encoders in cases of power failure, potentially leading to a loss of current position data if the turntable is not in its home position?
Does your turntable come equipped with a mechanical cam? If it does, you may notice a dead zone where the motor can continue spinning without the turntable moving, allowing for easy motor control with a proximity switch. This type of turntable I have experienced is a more efficient option compared to dealing with servos and the complexities of commissioning and programming them. The decision not to use it if you have it is purely practical - it requires additional work for everyone involved, from programming to troubleshooting when issues arise.
When working with motion control systems that utilize encoders, it is recommended to incorporate sensors to confirm the home position to detect any mechanical errors early on. By combining positional feedback from the encoder with proximity switches, you can create a system that stops at specific positions and verifies the encoder count within a defined range. This approach ensures accuracy and prevents potential issues. The turntable in question operates at a rate of 600-900 cycles per day, with a takt time of 56 seconds, allowing for a cycle time of 30 seconds. The design of the system is robust and can handle inertia and other mechanical factors efficiently. To ensure precise control, one approach is to use proximity switches for stop positions and rely on encoder position for controlling slow movements or overtravel. However, it is important to consider the use of incremental encoders and potential data loss in the event of a power failure, especially if the turntable is not at its home position.
Given the setup you've discussed, your best bet would be to leverage the benefits of your incremental encoder and inductive proximity switches. The encoder can effectively monitor the ongoing position of the turntable and respond to changes instantly, providing you with a robust control over rotation. Meanwhile, using inductive proximity switches would give you a reliable method to detect the absolute position – 'home' or 'end' positions. Now, overtravel protection is crucial to prevent any mechanical damage - a simple hard stop or limit switch could suffice here. And, to avoid any sudden stops, applying a slowdown or deceleration mechanism shortly before reaching the desired position sounds like a good idea. Incorporating a PID controller in your system might assist in slow deceleration and precision stopping. However, without specific details of your overall system and its objectives, it's hard to provide an optimal solution. It would be useful to know more about your product transfer rates, mass of products, tolerance for positioning, and safety requirements.
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Answer: - The optimal control methods for such a system typically involve utilizing the PowerFlex 525 0.4kW VFD for motor control, connecting it to the EK8S incremental encoder with 1024/4096 analog resolution, and wiring it back to an Allen-Bradley 1734-IK POINT I/O 24V DC Incremental Encoder Module. Factors to consider include using inductive proximity switches, implementing overtravel protection, and incorporating a slowdown mechanism before reaching the desired position.
Answer: - The rotation and stopping positions can be best controlled by programming the VFD and incremental encoder to work together effectively. Utilize the encoder feedback to ensure accurate positioning, set up the VFD for precise speed and direction control, and implement logic for stopping positions based on encoder feedback and overtravel protection mechanisms.
Answer: - When implementing control mechanisms for such a system, factors such as accurate positioning using the incremental encoder feedback, setting up appropriate speed profiles for rotation and stopping, incorporating overtravel protection to prevent damage, and including a slowdown mechanism for smooth
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