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【正文】 try. Modular machine tools have been on the market for a few of decades. The international standards became available to machine mod ules in the seventies [2]. Researchers have made continuous effort in improving modular machine tools. For example, Hannover University initialized a project called Modular Synthesis of Advanced Machine Tools (MOSYN) to support the design of customerspecific configurations of modular machine tools [3]. Nevertheless, it is worth to note that the primary objective of the machinetool builders to modularize their products is to produce the variants。 on other hand,machinetool users still purchase the systems with a specific configuration, and these systems are rarely reconfigured after their installments. Differing from traditional modular machine tools, the reconfigurable machine tool at the University of Michigan aims at modularity, integrability, customization, convertibility, and diagnosability. The system is designed to reconfigure frequently in a dynamic environment [46]. Unfortunately, the design concept was not fully implemented, and some obstacles slowed down their research and development [7]. The reconfigurable Parallel Kinematic Machine (PKM) is another alternative to reconfigure machine tools [810]. Theoretically, PKMs have the potentials to achieve higher speed, higher accuracy, and deal with a heavier load. However, the characteristics of the PKMs have not been well studied. Most of the mercially available PKMs are highcost machines that provide lower accuracy than conventional machine tools [7, 11]. More studies are on demand to develop petitive PKMs. For example, Zhao et al. [12] introduced a new parallel simulator with six degrees of freedom (DOF)。 this new PKM adopts redundant actuations to increase the capacity to resist external load and prolong the actuators’ of inverse kinematics for a redundant robot is often addressed by the pseudo inverse method。 Wang et al. expanded this method as a resolution for the redundant relations at velocity and acceleration levels,so called closedloop inverse kinematics algorithm was proposed to control a 7DOF redundant PKM [13]. Yun and Li developed the stiffness models for the flexure hinges [14]。 their work has its significance in predicting the deflections and improving the precision of PKMs. Researchers have continued in making progress on reconfigurable robotic systems. For example, a type of squarecubiccell module has been designed as the basic element to build various robotic configurations for different application. The targeted configurations can be open loop, closed loop, or a bination of both [15]. To develop a costeffective PKM machine tool, the tripodbased PKM is focused due to its two significant merits, that is, the versatility and the benefits of a closedloop mechanism. Tripodbased PKMs are the most versatile one among the existing PKMs. A tripodbased PKM typically possesses three DOF. Depending on its structure, it can produce an endeffector motion with the pure rotation, the pure translation, or a bination of rotation and PKMs can perform many different machining operations since the majority of the machining operations require a motion with five or less DOF [9]. A tripodbased PKM can be used as a stand alone machine or a module in a system. As a standalone machine, it can be a substitution of a traditional machine tool with three or less a system module, it can be bined with other actuated modules or subsystems. A new tripodbased machine with a passive leg has been proposed by the author,and the details of design method ologies and assistive design toolbox have been reported [16, 17]. In this paper,the control method and implementation of this machine tool will be focused. The remainder of the paper is organized as follows. In Section 2, the hybrid machine structure is introduced, the parallel structure for positioning is specially examined, and its kinematic model is over viewed. In Sections 3 and 4, the requirements of system control are discussed, and control architecture is proposed accordingly. The control model is developed for the machine tool,and the implementation of system control is discussed. In Section 5, a calibration approach for system reconfiguration is introduced. Finally in Section 6, the research works presented in this paper are summarized.2. Structure of FiveDOF Reconfigurable Machine Tool Figures 1(a) and 1(b) have illustrated the virtual model and physical model of the new hybrid reconfigurable machine tool, respectively. This machine tool consists of three modules: a tripod tool, an XY table, and a reconfigurable arch. This machine tool is hybrid, the positioning structure is a tripodbased PKM with three DOF, and the orienting structure is a serial wrist with two DOF. The tripodbased PKM is the most important modularized tripodbased PKM includes three linear actuators。 these actuators can be reconfigured and integrated with the custom is able base and endeffector platforms. The geometries of the base and endeffect or platforms can change the behaviours of the parallel structure significantly. The tripodbased PKM structure is expected to provide the rotations about X axis and Y axis and the translation along he Z axis. Reconfigurability of the machine tool can be further enhanced by the adjustments of the XY table and reconfigurable arch. Both of them are reconfigurable. The XY table provides various motion ranges of translation along X and Y axes, and its height along the Z axis can be reconfigured offline. The arch is an assembly of three ponents: two vertical columns and a horizontal beam. The orientation of the horizontal beam can be reconfigured to acmodate the changes of location and orientation of the working volume.The variations of the reconfigurable machine tool are from some customerized modules in the system. The dimensions of these modules such as binary legs and the platforms can be cust