Wire-driven Parallel Robot: Open Issues
Wire-driven parallel robot (WDPR) is a special class of parallel robot in which the rigid legs are replaced by wires, with potential advantages in terms of intrusivity and workspace. Although the study of WDPR seems to be a well-addressed subject, we will
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Wire-driven parallel robots
Wire-driven parallel robot (WDPR) is a special class of parallel robot in which the rigid legs are replaced by wires. As for classical parallel robot, motion of the platform may be obtained either by changing the lengths of the wires (type 1) or having fixed wires lengths and modifying the location of the attachment point A of the wires on the base (type 2). In the first case wire lengths may be modified by using either a coiling winch or by using a linear actuator with a pulleys system (Merlet, 2010). We may also distinguish completely restrained robot where the wires fully constrained the n d.o.f. of the platform (in which case the number of wire must be at least n + 1 (Ming et al., 1994)) and cable suspended robot with at least n wires, gravity playing the role of a virtual downward pulling wire. WDPR have been introduced in the 80’s (Landsberger and Sheridan, 1985),(Miura and Furuya, 1984) as an alternate to parallel robot with rigid links. The foreseen advantages was less intrusive legs, a simpler mechanical structure (passive joints are eliminated) and potentially larger workspace for the type 1, as the amount of leg lengths variation may be much larger than with rigid legs. WDPR shares with classical parallel robots the ability to manipulate large load and to be energy efficient. But the major difference is that wires can be pulled but not pushed, which imposes an unilateral constraint: that must be checked. We will see that this constraint greatly complexifies the analysis of WDPR. ∗
The author acknowledges the partial support of the EU through the grant 285404 CableBOT CP-FP
V. Padois, P. Bidaud, O. Khatib (Eds.), Romansy 19 – Robot Design, Dynamics and Control, CISM International Centre for Mechanical Sciences, DOI 10.1007/978-3-7091-1379-0_1, © CISM, Udine 2013
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J. P. Merlet and S.A. Inria
Several prototypes have been built in the 90’s, among them the famous ROBOCRANE (Albus et al., 1993), the FALCON robot (Kawamura et al., 1995) and the rescue robot of Tadokoro (Tadokoro et al., 1999), while the principle was partly patented (Thompson and Campbell, 1996). In the 2000’s further prototypes have been developed such as the SEGESTA robot (Hiller et al., 2005) and other prototypes (Barrette and Gosselin, 2005),(Fattah and Agrawal, 2005). Recently there has been a renewal of interest for WDPR in view of new applications: wind tunnel (Yaqing et al., 2007), biomechanic and rehabilitation (Wu et al., 2011), haptic interface (V. Zitzewitz et al., 2009), rescue robotics(Merlet and Daney, 2010) and telescope (Z-F et al., 2011) to name a few. Type 2 robots are illustrated in (Michael et al., 2009) in which several quadrotors are used to tow a load. In spite of all these works it appears that many issues that have been investigated for such robots need to be revisited as they are not fully understood.
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Kinematics
We first define the wire configuration of a WDPR at a pose as the set of wire numbers which are under tension. Clearly the unilateral constraint imposed on wires requ
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