Shape Sensing and Kinematic Control of a Cable-Driven Continuum Robot Based on Stretchable Capacitive Sensors.

A Cable-Driven Continuum Robot (CDCR) that consists of a set of identical Cable-Driven Continuum Joint Modules (CDCJMs) is proposed in this paper. The CDCJMs merely produce 2-DOF bending motions by controlling driving cable lengths. In each CDCJM, a pattern-based flexible backbone is employed as a passive compliant joint to generate 2-DOF bending deflections, which can be characterized by two joint variables, i.e., the bending direction angle and the bending angle. However, as the bending deflection is determined by not only the lengths of the driving cables but also the gravity and payload, it will be inaccurate to compute the two joint variables with its kinematic model. In this work, two stretchable capacitive sensors are employed to measure the bending shape of the flexible backbone so as to accurately determine the two joint variables. Compared with FBG-based and vision-based shape-sensing methods, the proposed method with stretchable capacitive sensors has the advantages of high sensitivity to the bending deflection of the backbone, ease of implementation, and cost effectiveness. The initial location of a stretchable sensor is generally defined by its two endpoint positions on the surface of the backbone without bending. A generic shape-sensing model, i.e., the relationship between the sensor reading and the two joint variables, is formulated based on the 2-DOF bending deflection of the backbone. To further improve the accuracy of the shape-sensing model, a calibration method is proposed to compensate for the location errors of stretchable sensors. Based on the calibrated shape-sensing model, a sliding-mode-based closed-loop control method is implemented for the CDCR. In order to verify the effectiveness of the proposed closed-loop control method, the trajectory tracking accuracy experiments of the CDCR are conducted based on a circle trajectory, in which the radius of the circle is 55mm. The average tracking errors of the CDCR measured by the Qualisys motion capture system under the open-loop and the closed-loop control are 49.23 and 8.40mm, respectively, which is reduced by 82.94%.

A flexible dual-mode sensor with decoupled strain and temperature sensing for smart robots.

Flexible dual mode strain-temperature sensors that mimic human skin functions are highly desired for wearable devices and intelligent robots. However, integrating dual sensing characteristics into a single sensor for simultaneous and decoupled strain-temperature detection still remains a challenge. Herein, we report a flexible dual-modal sensor that uses a "neutral surface" structural design technique to integrate an independently prepared temperature sensing layer (TSL) and strain sensing layer (SSL), for simultaneous monitoring of strain and temperature, in a decoupled manner. The TSL consists of a PDMS/BaTiO3 based dielectric layer whose dielectric constant and thickness change in response to temperature fluctuations. The SSL consists of a resistive type Ni80Cr20 film whose resistance changes in response to external strain. After optimizing the temperature and strain sensing characteristics of the TSL and SSL, the obtained dual-modal flexible sensor has shown a broad temperature sensing range (30 to 200 °C), with high temperature sensitivity (-160.90 fF °C-1), excellent linearity (0.998), and highly discernible temperature resolution (0.1 °C). Additionally, the sensor has also exhibited a wide strain monitoring range (20 to 1000 µÎµ), good strain resolution (20 µÎµ or 0.002%), and a fast strain response time (54 ms). When practically demonstrated, our sensor has successfully shown independent perception of strain and temperature, which highlights its promising application potential in the fields of smart robotics and intelligent prosthetics.

Sensors and Sensor Fusion Methodologies for Indoor Odometry: A Review.

Although Global Navigation Satellite Systems (GNSSs) generally provide adequate accuracy for outdoor localization, this is not the case for indoor environments, due to signal obstruction. Therefore, a self-contained localization scheme is beneficial under such circumstances. Modern sensors and algorithms endow moving robots with the capability to perceive their environment, and enable the deployment of novel localization schemes, such as odometry, or Simultaneous Localization and Mapping (SLAM). The former focuses on incremental localization, while the latter stores an interpretable map of the environment concurrently. In this context, this paper conducts a comprehensive review of sensor modalities, including Inertial Measurement Units (IMUs), Light Detection and Ranging (LiDAR), radio detection and ranging (radar), and cameras, as well as applications of polymers in these sensors, for indoor odometry. Furthermore, analysis and discussion of the algorithms and the fusion frameworks for pose estimation and odometry with these sensors are performed. Therefore, this paper straightens the pathway of indoor odometry from principle to application. Finally, some future prospects are discussed.

Mechatronics design and testing of a cable-driven upper limb rehabilitation exoskeleton with variable stiffness.

In this paper, we present a cable-driven exoskeleton with variable stiffness for upper limb rehabilitation. Adjustable stiffness of the cable-driven exoskeleton is achieved by attaching a novel variable stiffness module (VSM) to each driving cable. The module is able to vary stiffness in a large range through changing cable tension. In this paper, a stiffness model is developed for a cable-driven exoskeleton to reveal the stiffness performance of the exoskeleton with the influence of VSMs. Based on the stiffness model, a controller with stiffness-oriented strategy is proposed to vary the stiffness of the exoskeleton. Experiments on a prototype of a cable-driven exoskeleton are conducted to validate the controller.

The design and kinetostatic modeling of 3PPR planar compliant parallel mechanism based on compliance matrix method.

Compliant Parallel Mechanisms (CPMs) are widely used in micro/nano-positioning systems. In recent years, CPMs with a large travel range (≥1 mm) have been getting increasing attention. In this paper, a 3 Prismatic-Prismatic-Revolute (3PPR) planar CPM with a motion range of 5 mm × 5 mm × 5° is designed. The mechanical structure is characterized by the application of three joints based on a compliant four-bar mechanism, which guarantees the motions along/about the specific axes to improve motion accuracy. A double blade rotary pivot is served as a revolute joint to decrease the drift of pivot and produce a large rotation range without loss of compactness. The compliance matrix method is implemented to kinetostatic modeling, and the input coupling effect, which is always neglected or modeled complicatedly in 3-Degree-of-Freedom planar CPMs, is involved with the principle of superposition. The feasibility of the mechanical design and the accuracy of the developed kinetostatic model are validated by finite element analysis and experiments, respectively. The results indicate that the modeling method based on the compliance matrix method is concise, effective, and accurate, and can be extended to other more complicated CPMs.