This paper discusses the effect of axial backbone compression on tendon-driven continuum robots. A new mechanics model for compensating for this effect that does not require tendon tension sensing or knowledge of manipulator material properties/stiffnesses is introduced and analyzed. In addition, we provide an analytical expression for the minimum preload on the tendons to achieve a given bend, a quantity determined empirically thus far. Our model is computationally efficient and achieves real time control on low cost hardware. The analysis is supported by experimental results demonstrating significant improvement over kinematics in open loop control of a tendon-driven continuum hose robot.

In this paper, we present a new approach to the control of continuum robot sections using IMU quaternion feedback. We use a discrete time root finding algorithm to steer a continuum section in the desired shape space direction. We found that the approach lacks end effector positioning accuracy when used by itself, however, when used in conjunction with a feedforward model it actively counters the influence of unmodeled factors. The approach is implemented on a single section of a continuum hose robot developed for 3D printing of concrete in construction applications. The results demonstrate significant improvements in positioning accuracy compared to standalone kinematics/mechanics-based position control of tendon lengths. Additionally, this approach can be implemented using low cost sensing and control hardware.

We present a novel application of continuum robots acting as concrete hoses to support 3D printing of cementitious materials. An industrial concrete hose was fitted with a cable harness and remotely actuated via tendons. The resulting continuum hose robot exhibited non constant curvature. In order to account for this, a new geometric approach to modeling variable curvature inverse kinematics using Euler curves is introduced herein. The new closed form model does not impose any additional computational cost compared to the constant curvature model and results in a marked improvement in the observed performance. Experiments involving 3D printing with cementitious mortar using a continuum hose robot were also conducted.