Control and Tension Estimation of a Cable Driven Mechanism Under Different Tensions

Abstract

This paper proposes a method to estimate and compensate for the changes of cable tension in the control of cable driven mechanisms. Cable tension may depend on various factors, including mechanism design, fabrication and operation. In many systems it is also an adjustable parameter that affects the performance of the control system. An implementation of the unscented Kalman filter is used for the simultaneous estimation of the states and parameters of a cable driven mechanism. Changes in cable tension are captured in the estimated parameters which, along with system states, are used by a model predictive controller to generate appropriate control actions. The method is described and its effectiveness is shown for a single degree of freedom cable driven robot. In addition, the correlation between the cable tension and the estimated robot parameters provides a way of estimating the tension. It is shown that cable tension can be inferred from one of the estimated robot parameters, namely cable stiffness.

Unscented Kalman Filter and 3D vision to improve cable driven surgical robot joint angle estimation

“…2) Dynamic Model Parameters: Over time, the cable parameters such as stiffness and damping can change due to creep and stretch [7], [12]. We used the dual UKF parameter estimation and stereo vision offline to compensate for these changes to improve system dynamics.…”

“…Also, in a fully cable driven manipulator, sensitive parts are located away from the end-effector, which is then suitable for harsh environments [4], [5], [6]. In RSAs, due to sterilization, placement of tracking sensors or encoders on the end-effector is difficult [7]. In Raven, all the encoders are mounted on the shaft of the motors away from the joints.…”

“…However, the use of cable in robot manipulators introduces new challenges to control of the systems due to elasticity of cables and their nonlinear properties [7]. Moreover, cables transmits power thorough tension and therefore to treat them as a rigid link, the cables must remain under tension [7], [5].…”

“…Moreover, cables transmits power thorough tension and therefore to treat them as a rigid link, the cables must remain under tension [7], [5]. Also, compared to rigid links, the stiffness of cable is lower, which may cause undesirable vibrations [5] and a relative position error between motor and link [7]. If cable elasticity is not modeled in dynamic equations and an appropriate control compensation is not considered, the accuracy of a cable driven robot is limited.…”

UKF-Based Motion Estimation of Cable-Driven Forceps for Robot-Assisted Surgical System

“…However, the linear identification model has limitations in the presentation of the nonlinear characteristics of cabledriven systems. In order to approximate the system nonlinearity, the Unscented Kalman Filter (UKF) method was adopted to explore the motion estimation of cable-driven end joints [26], [27], and further implemented the motion control and external forces estimation [28], [29]. These studies have revealed that the joint motion estimation is critical for the high-precision motion control of surgical instruments when there are no sensors installed on the end joints or slender tool shaft.…”