Modeling and Control of a Cable-Suspended Sling-Like Parallel Robot for Throwing Operations

Abstract

Cable-driven parallel robots can provide interesting advantages over conventional robots with rigid links; in particular, robots with a cable-suspended architecture can have very large workspaces. Recent research has shown that dynamic trajectories allow the robot to further increase its workspace by taking advantage of inertial effects. In our work, we consider a three-degrees-of-freedom parallel robot suspended by three cables, with a point-mass end-effector. This model was considered in previous works to analyze the conditions for dynamical feasibility of a trajectory. Here, we enhance the robot’s capabilities by using it as a sling, that is, by throwing a mass at a suitable time. The mass is carried at the end-effector by a gripper, which releases the mass so that it can reach a given target point. Mathematical models are presented that provide guidelines for planning the trajectory. Moreover, results are shown from simulations that include the effect of cable elasticity. Finally, suggestions are offered regarding how such a trajectory can be optimized.

Dynamic Launch Trajectory Planning of a Cable-Suspended Translational Parallel Robot Using Point-to-Point Motions

“…In our tests, we have verified that the concept of using throwing trajectories (releasing an object from an EE suspended by cables) can indeed enlarge the workspace of CSPRs. The general concept has been proposed in our previous works [47,48], which however did not include an experimental section; additionally, those works only considered a simpler, less realistic model with a point-mass EE, while here we introduce a practically feasible design. To the best of our knowledge, no other works have considered CSPRs for throwing motions.…”

“…Based on concepts from [43], combined with the intrinsic advantages of CSPRs (such as a relatively high flexibility in trajectory design), we propose the use of CSPRs to perform launch motions, so that an object can reach target points far away from the robot base. In previous works [47,48], we analyzed a case in which the robot starts from a stationary state, slowly reaches a target elliptical motion through a transition trajectory (with gradually increasing amplitudes), and then completes the launch while moving along the elliptical trajectory. This choice in the trajectory design phase allowed us to directly reuse previous results on dynamically-feasible motions [24,31]; moreover, the trajectories thus found are general and flexible enough for application.…”

“…Setting p b = p T and ṗb = ṗT from Equations (26a) and (26b) fully defines the parabolic trajectory. On this parabola, we pick a launch point P L : this can be chosen either arbitrarily or through optimization, by searching the position of P L along the parabola that minimizes objective functions, such as the total energy and time requested for the launch [47]. The speed at the launch point is then found by solving Equation (26b) for the unknown ṗL .…”

Modelling and Control of Mechatronic and Robotic Systems

“…The authors in [9] present the modelling and control of a cable-suspended sling-like parallel robot for throwing a mass at a suitable time. The mass is carried at the end-effector by a gripper, which releases the mass so that it can reach a given target point.…”

Static Workspace Computation for Underactuated Cable-Driven Parallel Robots

“…If the set of wrenches is limited to the gravitational one, the constraint becomes static-feasibility [29], and allows one to determine the workspace where the manipulator can be brought to rest. On the other hand, recent studies also considered inertial actions among the wrenches applied to the EE, thus defining the concept of dynamic WS [30,31].…”