Bending Cycles and Cable Properties of Polymer Fiber Cables for Fully Constrained Cable-Driven Parallel Robots

Abstract

In most practical applications for cable-driven parallel robots, cable lifetime is an important issue. While there is extensive knowledge of steel cables in traditional applications such as elevators or cranes, it cannot be easily applied to cable robots. Especially new polymer based materials behave substantially different, but also the conditions for the cable change dramatically. Cable robots have more bending points and a higher variability in cable force and speed than traditional applications. This paper presents a form of bending cycle analysis which can be applied to assess cable wear. This algorithm counts the number of bends per trajectory in each cable segment. The sum gives an indication how much wear a cable receives. Experiments are conducted on a cable robot using different kinds of polymer fibers. The results show that this method is successful in predicting the point at which a cable finally breaks.

Force Tracking Using Actuated Winches With Position-Controlled Motors for Use in Hydrodynamical Model Testing

“…Hereafter, when not specified, we use the non-weighted version of ( 14), that is, w k =1 for i∈{1,•••,m}. Later, we continue to use bold notation to refer to sampled sets when referencing (14). For example, we write θ w to mean (θ w,1 ,θ w,2 ,•••,θ w,m ) and sgn(θ w ) to mean (sgn(θ w,1 ),sgn(θ w,2 ),•••,sgn(θ w,m )) .…”

“…Assuming values that are close to the query point provide more information, we now find β t using the weighted least square (14) with y=θ w and X = 1 t…”

“…which is used to determineτ ws ,τ wc , andτ cs . Assuming that damping is dominated by the position feedforward delay-induced damping (11), a redundant and independent method to identify delays uses (14) with β= β 0 βθ w , X = 1θ w , and y=f . The delay between the two signals is then estimated by:…”

“…We now use (14) to fit a model for the slow-speed variations using β m = β 0 β sin β cos β sgn and X m = 1 sin(θ w ) cos(θ w ) sgn(θ w ) . The resulting model is shown in grey in Figure 14 and appears to follow the trend quite well.…”

“…Good models of the actuators are advantageous for accurate force control. The cable is typically made of polymer with a high strength to weight characteristic [14]. This is modelled as a linear spring in [15] and by nonlinear cable models in [10].…”