Evaluation of Torsional Oscillations in Paper Machine Sections
Torsional oscillations are a critical factor that significantly impact the performance of paper machine sections, influencing the bandwidth (BW) and damping of speed loops. These oscillations can be exacerbated by backlash in gear reducers, particularly when the drive operates under very low load torque conditions. This paper provides an in-depth evaluation of these effects within typical electromechanical drive trains used in paper machine sections.
Understanding Torsional Oscillations
Torsional oscillations refer to the twisting vibrations that occur along the axis of a rotating shaft. In paper machines, these oscillations can lead to performance issues, including variations in speed control and potential mechanical failures. The primary sources of these oscillations include the inherent mechanical properties of the drive train components and operational factors such as load torque variations.
Evaluating Two-Mass and Three-Mass Systems
The study examines torsional oscillations in both two-mass and three-mass systems, which represent common configurations in paper machine drive trains. A two-mass system typically consists of a motor and a load connected by a flexible shaft, while a three-mass system includes an additional intermediate shaft or coupling. By analyzing these systems, the paper aims to identify how different configurations and component properties affect torsional behavior.
Impact of Shaft Diameter and Length
The diameter and length of the shaft play crucial roles in determining the resonant frequencies of the system. Resonant frequencies are the specific frequencies at which the system naturally oscillates with the greatest amplitude. In the context of paper machines, these frequencies can be influenced by the mechanical design of the shaft, affecting the overall stability and performance of the drive train.
The paper evaluates the effects of varying shaft diameters and lengths in three typical sections of paper machines. These sections include the press section, the drying section, and the finishing section, each with unique operational demands and mechanical configurations.
Time-Domain Response Analysis
To provide a comprehensive understanding of the impact of torsional oscillations, the paper presents time-domain response plots. These plots illustrate how the system responds to different speed commands, such as step or ramp inputs. Key factors analyzed include speed response overshoot and the influence of reducer backlash.
Speed response overshoot refers to the extent to which the actual speed exceeds the desired speed during transient conditions. Reducer backlash, the slight movement allowed between gear teeth before they fully engage, can amplify torsional oscillations, particularly at low load torques. By examining these time-domain responses, the paper highlights the dynamic behavior of the drive system and its susceptibility to oscillations.
Design Guidelines for Minimizing Torsional Oscillations
Based on the findings, the paper offers mechanical design guidelines aimed at minimizing torsional oscillations in speed-controlled drive systems. These guidelines focus on optimizing the design of key drive train components, such as:
- Shaft Design: Selecting appropriate shaft diameters and lengths to avoid resonant frequencies that coincide with operational speeds.
- Gear Reducers: Minimizing backlash in gear reducers to reduce the potential for torsional oscillations.
- Couplings: Utilizing flexible couplings that can absorb and dampen torsional vibrations.
- Drive Control: Implementing advanced control strategies that can adapt to varying load conditions and mitigate the effects of oscillations.
Torsional oscillations present a significant challenge in maintaining the performance and reliability of paper machine sections. Through detailed evaluation and analysis of two-mass and three-mass systems, as well as the effects of shaft dimensions and gear reducer backlash, this paper provides valuable insights into the mechanisms driving these oscillations. The proposed mechanical design guidelines serve as a practical resource for engineers and designers seeking to enhance the stability and efficiency of speed-controlled drive systems in paper machines. By addressing the root causes of torsional oscillations, these guidelines contribute to the development of more robust and reliable paper production machinery.