Bowden-cable Angle Sensor (BoA Sensor)
This research proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. The proposed bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable’s inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The bend sensor is not affected by a bend curvature of up to 80.0 m_1, unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor.
Related papers and patents
Useok Jeong and Kyu-Jin Cho, "A Novel Low-Cost, Large Curvature Bend Sensor Based on a Bowden-Cable," Sensors, Vol.16, No.7: 961, Jun. 2016. [PDF]
Patent: Bending Sensor, 10-1856310
Reliability Analysis of a Tendon-driven Actuation for Soft Robots
The reliability of soft robotic devices will be the bottleneck that slows their commercialization. In particular, fatigue failure issues are a major concern. Thus, reliability should be taken into account from the earliest stages of development. However, to date, there have been no attempts to analyze the reliability of soft robotic devices in a systematic manner. When soft robots are employed to force transmission applications, reliability is typically a dominant issue, since soft robotic structures are constructed with soft material components; these materials have highly nonlinear properties that arise due to the large distribution in the material properties. Furthermore, reliability should be analyzed from the robot’s system down to the components using domain knowledge about the system; this requires a systematic approach. This study presents a framework for reliability analysis of soft robotic devices taking into account of a probability distribution that has not been considered before and examines a case study of a tendon-driven soft robot. This study focuses specifically on 1) concept design process, 2) lifetime analysis process, and 3) design and optimization process. A life model that considers distribution is proposed using accelerated life testing (ALT) based on analysis of the failure mechanism of the tendon-driven system. The tensile stress of the wire was varied during the experiment with different bend angles and output tension. The result was validated with different stress levels using a testbed to simulate an actual application. The proposed reliability analysis methodology could be applied to other soft robotic systems like pneumatic actuators to improve the reliability-related properties during the robot design stage, and the life model can be used to estimate the device lifetime under various stress conditions.
Related papers and patents
Useok Jeong*, Keunsu Kim*, Sang-Hun Kim*, Hyunhee Choi, Byeng Dong Youn#, Kyu-Jin Cho#, "Reliability Analysis of a Tendon-driven Actuation for Soft Robots," The International Journal of Robotics Research.
Sang-Hun Kim, Useok Jeong, Keunsu Kim, Hyunhee Choi, Byeng Dong Youn, Kyu Jin Cho, "Reliability and Degradation Analysis of Bowden-Cable Transmission for Soft Robotic Systems", 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft).