The optimal architecture of a cable-based robot for warehousing applications is the main topic of this paper. This study is limited to two types of redundant planar symmetrical configurations with crossed and non-crossed cables. The design problem is divided in two main stages. First, the feasible workspace is optimized for a maximum size and rectangular-type shape of each of the redundant planar architectures. A set of four parameters is selected to fully define the geometry of the mobile platform and the location of its anchor points. In the second design stage, an optimized spatial architecture is obtained for a maximum stiffness by selecting a new set of six parameters which defines the transversal anchor points on both the mobile and static platforms. Based on these optimal parameters, a prototype is fully modeled and built for further experimentation.

This paper presents and analyzes a novel architecture for a fully constrained cable-based robot that is used in warehousing tasks. A mobile platform is connected to a static box by a set of twelve cables; the cables arrangement allows the mobile platform to achieve stiff positions with constant orientation along with large planar motions. The mechanical analysis of the robot includes inverse and forward kinematics, as well as static analysis and stiffness models. In addition, a workspace analysis describes the feasible boundaries for the suspended and fully constrained cases. Then, the stiffness attributes for both cases are analyzed and discussed. Simulation results show that the proposed robot meets the warehousing requirements of large workspace, high stiffness, and low force input.

Cable-based robots generally perform better than other parallel robots with rigid links in terms of wider workspace and higher acceleration of end effector because of lightweight of robot links. Cable based robots allow an easy mounting and remounting for outside applications; however, this requires a precise assembly of components at the cable anchor points. In this study, firstly a parametric model is developed for estimation of position errors of anchor points for fully-constrained and redundant planar cable robots. A novel method based on inclusion of virtual cables facilitates the linear separation of the uncertain parameters from the input-output signals for redundant planar robots. In addition, the adaptive law (parameter estimator) updates the estimated parameters using the least squares algorithm. The simulation results show that the least squares method reduces the time of estimation convergence compared to gradient algorithms. Furthermore, the least squares method allows simple persistent excitation signals to estimate parameters.

This work deals with the design and comparison of two adaptive position control schemes with a classical PID controller for fully constrained and redundant planar robots. First, a novel method based on inclusion of virtual cables facilitates the linear separation of the uncertain parameters from the input-output signals. Then, two Lyapunov based adaptive controllers based on the sliding mode and PD schemes are designed to compensate for the structure matrix uncertainties, which result from errors in the anchor point locations. Finally, the adaptive controllers are evaluated and compared with a classical PID controller through simulations for a desired 2D singularity-free pose of the mobile platform. The simulation results have shown that the adaptive PD control scheme has the best performance for both fully constrained and redundant cases.

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