Today an efficient warehouse and inventory management of spare parts for production machinery is essential for service organizations. Optimal strategies in procurement, stocking and supply play an important role for serviceability in spare parts management. In this context, individual item criticality should be considered, which describes how crucial a spare part is. This paper presents a three-dimensional classification approach for spare parts regarding a cross-plant central warehouse strategy of a service network. The approach uses two dimensions to estimate value and predictability of spare parts with aid of an ABC and XYZ analysis. The third dimension VED analyses a multi-criteria criticality classification and six feasible criteria are identified to describe item criticality. The methodology of the analysis is based on a decision tree, which represents the defined criteria by nodes. In addition, the analytic hierarchy process is used to solve the multi-criteria decision problems at the different nodes of the decision tree. The approach is developed in a research project and evaluation of spare parts is performed based on real inventory and transaction data in cooperation with an industrial company. As a result 15,000 out of 50,000 items could be classified as suitable for central warehousing.
Compliant and precise rotary drive units are essential for the design of articulated robots that are capable of safe human-robot collaboration. In this paper, we present a new pneumatic rotary drive unit that combines the compliance of pneumatic systems with the ability to perform high precision positioning. We use pneumatic artificial muscles (PAMs) pulling on a swash plate to avoid the stick-slip phenomenon and to realize adjustable stiffness. Furthermore, the presented drive unit can operate in 360 • continuous rotation. These properties make the drive particularly suitable for the later use in humanrobot collaboration. We explain the mechanic design as well as the pneumatic and electric control system that we use to operate the drive unit. We derive the equations to calculate the static torque distribution and compare the theoretical results to the data measured on the realized laboratory test stand, depicted in figure 1. The accuracy of the used 16-bit encoder is achieved and adjustable stiffness is realized and measured on the laboratory test stand. The measurements of the reaction to a step response are discussed based on a first and basic control strategy.
Robots that enable safe human-robot collaboration can be realized by using compliant drive units. In previous works, different mechanical designs of compliant pneumatic rotary drive units with similar characteristics have been presented. In this paper, we present the overall control approach that we use to operate one of these compliant pneumatic rotary drive units. We explain the mechanical design and derive the differential equation that describes the dynamics of the system. In order to successfully operate a pneumatic drive unit with three or more working chambers, the torque specified by the controller has to be split up onto the working chambers. We transfer the well-known field-oriented control approach from electric motors to the investigated pneumatic drive unit to create such a torque mapping. Moreover, we develop optimized torque mappings that are tailored to work with this type of drive unit. Furthermore, we introduce and compare two control algorithms based on different implementations of state feedback to realize position control. Finally, we present the step responses that we achieve when we implement either one of the control algorithms in combination with the different torque mappings.
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