Michael Lorenz

Design methodology for translational parallel manipulators exhibiting actuation redundancy

In general, spatial manipulation of objects can be accomplished by parallel manipulators, whose number of actuators is equal to the demanded number of degrees of freedom. In order to improve, for example, positioning accuracy, stiffness characteristics, and transmission behavior, redundant drives can be added to the manipulator. Accordingly, this paper presents a methodology for the design of a translational parallel manipulator with redundant actuation. Based on the results of systematic structural syntheses and developed selection criteria, two valid configurations (i.e. 3-PŘŘŘ and 3-PUU) are analyzed. Since feasibility and performance of these configurations are dependent on the base geometry, five types of base geometries are introduced. First, the geometric parameters of each of the resulting 10 combinations of nonredundant configurations and base geometries are optimized by minimizing the maximal actuation force within a prescribed workspace. Second, the best combinations are used to generate redundant configurations with six legs. These redundant configurations are then analyzed with respect to the potential of improvement concerning homogenization of end-effector forces using force polytopes. It is shown that redundant actuation significantly improves the distribution of end-effector forces. This improvement has a positive influence on positioning accuracy and acceleration capabilities. In addition to these aspects, for further analysis it is planned to investigate the influence of homogenized end-effector forces on the dimensioning of actuators and finally on the energy efficiency of the entire configuration.

Kinetostatic Performance Analysis of a Redundantly Driven Parallel Kinematic Manipulator

In general the mechanical handling of objects in space is performed by manipulators, whose number of actuators is consistent with the number of required degrees of freedom. In addition, manipulators can be equipped with redundant drives, providing the manipulator with more actuators than the mobility actually requires. Thus, an active distribution of drive torques is enabled.Accordingly, this research intends to analyze the effects of torque distribution in over-actuated manipulators relating to load-optimized and energy-efficient handling. By developing torque distribution strategies the maximum torque levels can be reduced and the required drive power thus be decreased. This results in an increased drive utilization, which improves the energy-efficiency of the handling system. On this basis, an innovative handling concept is analyzed, which represents an over-determined system given the number of actuators. Hence, it is shown that the drive utilization of manipulators can be significantly improved by means of actuation redundancy. For this purpose different mathematical optimization approaches are analyzed, which solve the over-actuated system with defined optimization targets. Here, the optimal torque distribution is found using an algorithm, which minimizes the maximum torque for each object position. The results demonstrate the efficiency of active torque distribution in terms of over-actuated manipulators. For a further approach it is planned to develop control methods including optimized torque distribution strategies in order to improve the performance and the energy efficiency of the entire manipulator.Copyright

Synthesis and Modeling of Redundantly Actuated Parallel Kinematic Manipulators—An Approach to Efficient Motion Design

Spatial object manipulation is subject to various parameters, which can be optimized by means of suitable motion strategies. In addition, corresponding strategies can be adapted to specified handling devices enabling efficient motion design with respect to kinematic and dynamic characteristics of particular manipulators. Further optimization is provided by the application of robot redundancy, whose resolution can be adapted to efficient motion planning. In this context, parallel kinematic systems featuring kinematic redundancy or a redundant actuator concept can be operated with an optimal set of actuator parameters allowing a resource-efficient object manipulation. This contribution is devoted to the conception and modeling of redundantly actuated parallel kinematic manipulators (RA-PKM) in order to realize optimal configuration strategies and motion design. Accordingly, the structure selection and the dimensional synthesis of a translational RA-PKM are presented based on parametric kinematic and dynamic modeling. Corresponding models provide an application-oriented transformation from intuitive CAD design software to technical computing and simulation software. The developed manipulator is suitable for the comparison of different redundant and non-redundant actuator configurations as well as optimal trajectories. Concluding analyses exemplarily refer to a non-redundant 3-arm and a redundant n-arm PRPaR system.

Industrial energy efficiency potentials: an assessment of three different robot concepts

Abstract The rise in energy consumption and the associated costs instigate financial concerns among industrial energy consumers. For industrial processes addressing heating and cooling as well as material transformation, a wide range of energy efficiency measures have been developed and successfully implemented. In contrast to that, most robot-based operations such as pick-and-place motions or assembly tasks still use inefficient standard concepts causing high-energy consumption and high-energy costs. Thanks to a rather low payload-to-weight ratio of new robot designs, such as parallel kinematic or hybrid robot manipulators, a high potential for energy savings is expected. This article identifies potentials for energy saving concerning industrial consumers by assessing three different robot concepts. Based on a literature review, two existing designs for robots – the conventional serial robot and the parallel kinematic robot are analysed and compared with respect to the energy utilised during a typical item placement task. Afterwards, the concept of PARAGRIP, a hybrid of the two presented robot designs is introduced and examined based on simulation regarding its energy consumption. The final results demonstrate significantly different energy consumptions between the robot concepts, identifying potential savings of about 40% in a selected industrial application scenario.

Study of Redundantly Actuated DELTA-Type Parallel Kinematic Mechanisms

Due to their high precision and dynamic properties, parallel kinematic manipulators (PKM) are particularly suited for high-speed and high-accuracy object handling. In order to improve their stiffness, their payload capacity and their accuracy PKM can be optimized using a redundant actuator configuration. Accordingly, additional actuators are added to PKM to generate an optimized performance. The objectives, in this context, are highly task oriented and can involve a wide range of the robot’s topological and morphological parameters. Based on different tasks and optimization objectives, robots with unique specifications can be designed. In this study redundancy is used to show the effect of topological parameters of redundantly actuated DELTA-type parallel manipulators on general performance characteristics, such as the energy consumption of the robot. The topological characteristics of n-RRPaR manipulators in combination with actuator capabilities are considered as variables. It is shown that optimal torque distribution, chosen a proper topology, would enhance the manipulator’s performance and may result in a more efficient energy consumption.

Power manipulability analysis of redundantly actuated parallel kinematic manipulators with different types of actuators

Spatial object manipulation is typically accomplished by parallel kinematic manipulators (PKM), whose number of actuators is equal to the required number of degrees of freedom. In order to improve the performance and reliability of PKM, their basic configuration can be extended by redundant actuators. This paper is devoted to the special case of PKM with both linear and rotational actuation, which can be operated simultaneously. Corresponding manipulators face the problem of coexisting translational and rotational joint space parameters inducing inhomogeneous Jacobian matrices. In this context, power manipulability ellipsoids provide a suitable performance evaluation for PKM featuring different types of redundantly applicable actuators. Accordingly, this research intends to analyze the kinetostatic performance of redundantly actuated PKM and to demonstrate their efficiency in contrast to non-redundant drive configurations. The analyses exemplarily are focused on the translational 3-RPC manipulator, since it can be equipped with both revolute and/or prismatic joint actuation.

Design, Construction and Testing of a Gripper for Horticulture Products

This paper describes the design of a gripper for grasping and manipulating horticulture products. The design solution has been achieved by means of a systematic approach, by evaluating all the possible architectures to get an optimal one. The proposed structure is numerically designed and simulated and then a prototype has been built and successfully tested in laboratory.