Design and dynamic analysis of three degrees of freedom desk-top reconfigurable machine
ABSTRACT This paper presents the development of three degrees of freedom (DOF) desk-top reconfigurable machine tool. Recently, numerous components or systems in various areas such as biomedical, Micro-Electro-Mechanical Systems (MEMs) often require dedicated and precise but cost efficient manufacturing process along with large fluctuations of product demands in a global market. These demands lead us to develop a downscaled desk-top manufacturing machine which reduces the size of a machine but offers to control multi-DOF motions rapidly and smoothly. In this paper, we first introduce the design concept of three DOFs desk-top reconfigurable machine and analyze both static and dynamic structure characteristics. The results show feasibility that the position and orientation of the machine tool can be controlled during the machining operation simultaneously. Then, the dynamic simulations and experimental results using a closed loop control with a position feedback are presented to demonstrate performance and feature of the system. Unlike conventional full scaled manufacturing machines, the machine developed here provides a number of advantages; light weight and fast dynamic response, simple design and low cost, compact but relatively large workspace without motion singularity.
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ABSTRACT: This paper deals with the conceptual design and dimensional synthesis of a 3-DOF parallel mechanism module which forms the main body of a newly invented 5-DOF reconfigurable hybrid robot named "TriVariant." The TriVariant is a modified version of the Tricept robot, achieved by integrating one of the three active limbs into the passive limb. The idea leading to the innovation of the module is systematically addressed. Its kinematic performance is optimized by minimizing a global and comprehensive conditioning index subject to a set of appropriate mechanical constraints. It is concluded that the proposed hybrid system is more cost-effective and has a competitive kinematic performance in comparison with the well-known Tricept robot.IEEE Transactions on Robotics 07/2005; · 2.57 Impact Factor
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ABSTRACT: Reconfigurable manufacturing systems (RMS) address challenges in modern manufacturing systems arising from product variety and from rapid changes in product demand. This paper considers an arch-type reconfigurable machine tool (RMT) that has been built to demonstrate the basic concepts of RMT design. The arch-type RMT was designed to achieve customized flexibility and includes a passive degree-of-freedom, which allows it to be reconfigured to machine a family of parts. The kinematic and dynamic capabilities of the machine are presented, including the experimental frequency response functions (FRFs) and computed stability lobes of the machine in different configurations. A comparison of FRFs and stability lobes of the arch-type RMT reveals almost similar dynamic characteristics at different reconfiguration positions. These similar characteristics arise because the dominant mode where chatter occurs is due to the spindle–tool–tool holder assembly. Consequently, to ensure consistent dynamic behavior regardless of reconfiguration, a desirable dynamic design feature for RMTs is that the machine's structural frequencies are less dominant than the structural frequencies of the spindle, tool and tool holder.International Journal of Machine Tools and Manufacture. 01/2007;
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ABSTRACT: This paper presents the effects of the torque model on the control of a variable reluctance spherical motor (VRSM) that offers several attractive features by combining multi-DOF motions in a single joint. A general form of the torque model for a VRSM is derived using the principle of energy conversion. The torque models for two specific design configurations developed at Georgia Tech are compared. The first has been based on an existing design characterized by a torque model in quadratic form. For feedback control of the spherical motor, the quadratic form of the torque model requires the use of nonlinear optimization schemes for computing the stator coil current inputs. The second design incorporating high coercive permanent magnets has a linear torque–current relationship and thus allows a closed form solution for both forward and inverse torque models. The effects of the torque model on a PD-controlled VRSM prototype has been studied both numerically and experimentally. Experimental results agree well with the computation derived analytically.Control Engineering Practice. 01/2004;