ECODWELL: Efficient Generation of Dwells in Highly Dynamic Machines
Motivation
With the goal of the Climate Protection Plan 2050 to limit global warming to 1.5°C research is being undertaken in many industrial sectors to make machines, processes and technologies more energy efficient. Due to rising energy prices, increasing energy efficiency is also becoming more important economically.
Production machines often perform their tasks with the help of motion systems. Operation in so-called Eigenmotion is one way to increase the energy efficiency of motion systems.
Almost exclusively cam mechanisms are used for dwell mechanisms. Here, there is great potential for saving energy, since such mechanisms, which are found in highly dynamic machines such as weaving machines, printing machines or packaging machines, often run in multi-shift operation.
The actuation of a classic cam mechanism with a constant input speed is common for dwell motions, as the cam allows an almost arbitrary movement of the follower and is still quite robust. Also used in various machines are dwell mechanisms based on a planar linkages without a cam disc and with a constant input speed. These mechanisms can produce approximate dwells. However, they do not allow arbitrary movement between dwells, as this movement is predefined by characteristics of the mechanism. The last combination of the prior art is the direct generation of the output motion by a variable control without a mechanical component (for example by a servo drive). As servo drive technology is rapidly evolving, this combination is becoming more attractive for industrial applications. However, this combination requires powerful drives, which reduce the cost-effectiveness of this solution due to the high costs involved.
Goal
During this project, a strategy for developing efficient dwell mechanisms for highly dynamic applications will be elaborated. The possibilities of optimally combining electrical and mechanical components will be demonstrated. In contrast to these classical combinations for generating a dwell movement, the control of a dwell mechanism with variable input movement has many advantages. On the one hand, the mechanism can be actuated in its Eigenmotion. Driving a mechanism in its Eigenmotion is very energy efficient because no energy is needed to overcome the inertial forces. Therefore, the servo motor can be scaled down. In contrast to the classic dwell mechanism without a cam, exact dwells can be realised by specifying an input speed of zero during the dwell. The dwell can be extended by braking the drive while the mechanism is at rest. This effect can be used to reduce the dimensions of the cam or to increase the transmission angles and thus reduce the required transmission torque. Despite these advantages, these combinations have hardly been explored so far.
Approach
To make the combinations and their advantages more available, this project will develop a guide for synthesising these combinations. This guidance will provide a strategy for the structural and dimensional synthesis of dwell mechanisms. This will include the synthesis of ways to provide a variable input speed. To assist the user in the process of structure synthesis, the combinations of servo motor, planar linkages and cam mechanisms are examined for their technical limitations. These limits help the user to exclude structures that do not meet the motion and economic requirements. The methods for the dimensional synthesis of the structures belonging to the state of the art are sufficiently described in the literature. The development of the methods belonging to the object of research is carried out within the scope of this project. Since these structures include a possibility to vary the input motion, the methods of power balancing can be used to increase the efficiency of the mechanism. Therefore, the dimensional synthesis includes not only the determination of the kinematic parameters of the mechanism, but also the determination of the inertial parameters. Since the mass of a link is directly related to its stiffness, the influence of flexible links must be analysed for this type of application. The validation of the methods and the proof of the advantages of the combinations within the research subject are put into practice by integrating the methods into the mechanism software MechDev as well as a physical model.