Within the last years, the robots with parallel structure Delta 3DOF are used more and more in applications that require: transporting objects at high speed, transporting heavy objects, at a high accuracy. Because the parallel structures have a limited workspace, researches on the workspace amplified lately. This work is approaching the study of determining the workspace for a parallel structure Delta 3DOF. The method being used allows the numerical determining of the workspace shape, as well as its limits. At the same time, this method helps with establishing the methods for optimizing the workspace so that the largest possible workspace is provided.
In the field of manufacturing processes it is observed that the trend is to produce more and more faster, efficiently parts with high complexity, which involves using a high number of tools in the machining process. One of the main solutions for high speed and efficient manufacturing is based on the full automation of the entire manufacturing process. The automatic changing of the tools involved in the manufacturing process is carried out by the automatic tool changing mechanism, thus the auxiliary non-productive time consumed with the tool change is highly minimized. In this paper we present a novel automatic tool changer which is both simple and compact, and any milling machining center provided with chain or disc tool magazine can be equipped with. Also by adopting the use of this tool changing mechanism other subassemblies of the tool changing system, such as the tool transfer mechanism and the waiting position, are substituted by this changing mechanism. The auxiliary movements needed to bring the tool from the magazine into the waiting position are overlapped with the machining time, so that the total time for exchanging the tool in the spindle with the tool from the magazine is minimized.
The latest milling machining centres have in their structure a rotary table which is used for machining up to 5 faces of an workpiece using only one set-up. In order to meet the requirements of an workpiece, that are more and more precise, it is recommended to increase the positioning accuracy of the machine tool table and also the number of indexing points. In this paper we present a new rotary, palletizing table which is provided with 360000 indexing positions and at every 4x90° the indexing precision is ±1``. This solution can be integrated in the structure of milling machining centres which adopt pallets with the nominal size from 400x400 mm to 800x800 mm. The table rotation axis is closed-loop controlled and is actuated by a servomotor with variable speed. The presence of speed and position control in the table`s structure assures the obtaining of high quality indices superior to classic feed systems. The kinematic feed chain has in its structure a duplex worm gear which guarantees the transmission without mechanical clearances. Also the table is provided with a high precision pallet positioning and clamp/unclamp mechanism which attains a position repeatability of ±2``. The advantages of the presented solution find themselves in the general characteristics of the machining centre, providing it with new performances in increasing the precision of the machined workpiece.
In small and medium batch series manufacturing the small tool and workpiece changing time is one of the main objectives to follow in obtaining high productivity. These auxiliary times are defined as the times consumed with preparing and changing the next tool or workpiece to follow the machining process, times that usually overlap the machining process. For this purpose machining centres are equipped with an automatic tool changer system and an automatic pallet changer system. The palletizing systems imply eliminating the times consumed with the alignment, fixing and clamping of the workpieces, these systems consisting of several mechanisms: the pallet, the automatic pallet changing mechanism, the positioning mechanism and the pallet clamp/unclamp mechanism. In this paper we present an general overview of the automatic pallet changing mechanisms used both in flexible manufacturing systems and machining centres.
The use of machining centres is predominant in the case of small and medium size batch manufacturing, their advantages being materialised in high productivity. The productivity is owed, mainly, to the small auxiliary times consumed with the tool and material change, times which are served by the automatic tool changer system and the automatic pallet changer. The purpose of this article researches aims to determine the kinematic parameters of an hydraulically driven linear pallet changer in two cases (when the deceleration is carried out through a throttle and when the deceleration is made through a new solution). Thus, an experimental set-up, which matches an hydraulically driven linear pallet changer, was designed and built. The experiments aimed toward using a classic braking method of hydraulic cylinders and a new two-stage braking with counter-pressure limitation.
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